PART III SOLUTIONS TO REVIEW QUESTIONS AND EXERCISES

Transcription

1 PART III SOLUTIONS TO REVIEW QUESTIONS AND EXERCISES

2 Solutions to Review Questions and Exercises Part One Background 4 Chapter 1 Introduction to Databases... 4 Chapter 2 Database Environment... 6 Chapter 3 The Relational Model... 8 Chapter 4 Database Planning, Design, and Administration Part Two Methodology 14 Chapter 5 Entity-Relationship Modeling Chapter 6 Normalization Chapter 7 Methodology - Conceptual Database Design Chapter 8 Methodology - Logical Database Design for Relational Model Chapter 9 Methodology - Physical Database Design for Relational DBMSs Chapter 10 Conceptual Database Design Methodology - Worked Example Chapter 11 Logical Database Design Methodology - Worked Example Chapter 12 Physical Database Design Methodology Worked Example Part Three Database Languages 33 Chapter 13 SQL Chapter 14 Advanced SQL Chapter 15 QBE Part Four Selected Database Issues 47 Chapter 16 Security Chapter 17 Transaction Management Chapter 18 Query Processing Part Five Current Trends 62 Chapter 19 Distributed DBMSs - Concepts and Design Chapter 20 Distributed DBMSs - Advanced Concepts Chapter 21 Introduction to Object DBMSs Chapter 22 Object-Oriented DBMSs

3 Chapter 23 Object-Relational DBMSs Part Six Future Trends 89 Chapter 24 Web Technology and DBMSs Chapter 25 Data Warehousing Chapter 26 OLAP and Data Mining

4 Review Questions Part One Background Chapter 1 Introduction to Databases 1.1 List four examples of database systems other than those listed in Section 1.1. Some examples could be: A system that maintains component part details for a car manufacturer; An advertising company keeping details of all clients and adverts placed with them; A training company keeping course information and participants' details; An organization maintaining all sales order information. 1.2 Discuss each of the following terms: Data For end users, this constitutes all the different values connected with the various objects/entities that are of concern to them. (See also Section 1.3.3) Database (See Section 1.3.1) Database Management System (See Section 1.3.2) Data Independence Security Integrity Views This is essentially the separation of underlying file structures from the programs that operate on them, also called program-data independence. (See also Sections and 1.3.1) The protection of the database from unauthorized users, which may involve passwords and access restrictions. (See also Section 1.6) The maintenance of the validity and consistency of the database by use of particular constraints that are applied to the data. (See also Section 1.6) These present only a subset of the database that is of particular interest to a user. Views can be customized, for example, field names may change, and they also provide a level of security preventing users from seeing certain data. (See also Section 1.3.2) 1.3 Describe the approach taken to the handling of data in the early file-based systems. Discuss the disadvantages of this approach. Focus was on applications for which programs would be written, and all the data required would be stored in a file or files owned by the programs. (See also Section 1.2). Clearly, each program was responsible for only its own data, which could be repeated in other program s data files. Different programs could be written in different languages, and would not be able to access another program s files. This would be true even for those programs written in the same language, because a program needs to know the file structure before it can access it. (See also Section 1.2.2). 1.4 Describe the main characteristics of the database approach and contrast it with the file-based approach. Focus is now on the data first, and then the applications. The structure of the data is now kept separate from the programs that operate on the data. This is held in the system catalog or data dictionary. Programs can now share data, which is no longer fragmented. There is also a reduction in redundancy, and achievement of program-data independence. (See also Section 1.3) 1.5 Describe the five components of the DBMS environment and discuss how they relate to each other. See Section Discuss the roles of the following personnel in the database environment: 4

5 Data Administrator See Section Database Administrator See Section Logical Database Designer See Section Physical Database Designer See Section Application Programmer See Section End Users See Section Discuss the advantages and disadvantages of database processing. Exercises See Section Interview some users of database systems. Which DBMS facilities do they find most useful and why? Which DBMS facilities do they find least useful and why? What do these users perceive to be the advantages and disadvantages of the DBMS? Select a variety of users for a particular DBMS. If the users are using different DBMSs, group the answers for the different systems, which will give an overall picture of specific systems. 1.9 Write a small program that allows entry and display of renter details including a renter number, name, address, telephone number, preferred number of rooms and maximum rent. The details should be stored in a file. Enter a few records and display the details. Now repeat this process but rather than writing a special program, use any DBMS that you have access to. What can you conclude from these two approaches? The program can be written in any appropriate programming language, such as Pascal, FORTRAN, C. It should adhere to basic software engineering principles including being wellstructured, modular, and suitably commented. It is important to appreciate the process involved even in developing a small program such as this. The DBMS facilities to structure, store, and retrieve data are used to the same effect. The differences in the approaches, such as the effort involved, potential for extension, ability to share the data should be noted Study the DreamHome case study presented in Section 1.7. In what ways would a DBMS help this organization? What data can you identify that needs to be represented in the database? What relationships exist between the data? What queries do you think are required? It may be useful to review the file-based approach and the database approach here before tackling the first part of the exercise. Careful reading and thinking about how people might use the applications should help in carrying out the rest of the exercise Study the Wellmeadows Hospital case study presented in Appendix A. In what ways would a DBMS help this organization? What data can you identify that needs to be represented in the database? What relationships exist between the data? The approach used for Exercise 1.10 should be used for this exercise also. 5

6 Review Questions Chapter 2 Database Environment 2.1 Discuss the concept of data independence and explain its importance in a database environment. See Section To address the issue of data independence, the ANSI-SPARC 3-level architecture was proposed. Compare and contrast the 3 levels of this model. See Section What is a data model? Discuss the main types of data models. An integrated collection of concepts for describing data, relationships between data and constraints on the data in an organization. (See also Section 2.3). Object-based data models such as the entity-relationship model (see Section 2.3.1). Record-based data models such as the relational data model, network data model, and hierarchical data model (see Section 2.3.2). 2.4 Discuss the function and importance of conceptual modeling. See Section Describe the types of facilities you would expect to be provided in a multi-user Database Management System. Data Storage, Retrieval and Update A User-Accessible Catalog Transaction Support Concurrency Control Services Recovery Services Authorization Services Support for Data Communication Integrity Services Services to Promote Data Independence Utility Services See also Section Of the facilities in 2.4, which ones do you think would not be needed in a standalone PC Database Management System? Provide justification for your answer. Concurrency Control Services - only single user. Authorization Services - only single user, but may be needed if different individuals are to use the DBMS at different times. Utility Services - limited in scope. Support for Data Communication - only standalone system. 2.7 Describe the main components in a DBMS and suggest which components are responsible for each facility identified in question 2.5. Query Processor, DML Preprocessor, Query Optimizer, Data Manager Dictionary Manager Data Manager Scheduler Utilities Authorization Control Utilities Integrity Checker Database Manager, DDL Compiler, File Manager Data Storage, Retrieval and Update A User-Accessible Catalog Transaction Support Concurrency Control Services Recovery Services Authorization Services Support for Data Communication Integrity Services Services to Promote Data Independence 6

7 Utility Services See also Sections 2.5 and What is meant by the term "client-server architecture" and what are the advantages of this approach? Compare the client-server architecture with two other architectures. The client is a process that requires some resource, and the server provides the resource. Neither need reside on the same machine. Advantages include: Better performance Likely reduction in hardware costs Reduction in communication costs Better consistency See also Section Discuss the function and importance of the data dictionary. Exercises See Section Analyze the DBMSs that you are currently using. Determine each system s compliance with the functions that we would expect to be provided by a DBMS. What types of languages does each system provide? What type of architecture does each DBMS use? Check the accessibility and extensibility of the data dictionary. Is it possible to export the data dictionary to another system? To do this you will need to obtain appropriate information about each system. There should be manuals available or possibly someone in charge of each system who could supply information Write a program that stores names and telephone numbers in a database. Write another program that stores names and addresses in a database. Modify the programs to use external, conceptual, and internal schemas. What are the advantages and disadvantages of this modification? The programs can be written in any suitable language and should be well structured and appropriately commented. Two distinct files result. The structures can be combined into one containing name, address, and tel_no, which can be the representation of both the internal and conceptual schemas. The conceptual schema should be created separately with a routine to map the conceptual to the internal schema. The two external schemas also must be created separately with routines to map the data between the external and the conceptual schema. The two programs should then use the appropriate external schema and routines Write a program that stores names and dates of birth in a database. Extend the program so that it stores the format of the data in the database; in other words, create a data dictionary. Provide an interface that makes this data dictionary accessible to external users. Again, the program can be written in any suitable language. It should then be modified to add the data format to the original file. This should not be difficult, if the original program is well structured. The interface for other users operates on the data dictionary and is separate from the original program. A menu-based interface is adequate How would you modify this program to conform to a client-server architecture? What would be the advantages and disadvantages of this modification? The server should hold the data dictionary and the programs that operate on it. The user interface should be separate, on the client, and call the data dictionary programs. 7

8 Review Questions Chapter 3 The Relational Model 3.1 Discuss each of the following concepts in the context of the relational data model: (a) (b) (c) (d) (e) Relation Attribute Tuple Intension and Extension Degree and Cardinality. Each term defined in Section Discuss the differences between the candidate keys and the primary key of a relation. Explain what is meant by a foreign key. How do foreign keys of relations relate to candidate keys? The primary key is the candidate key that is selected to identify tuples uniquely within a relation. A foreign key is an attribute or set of attributes within one relation that matches the candidate key of some (possibly the same) relation. 3.3 Define the two principal integrity rules for the relational model. Discuss why it is desirable to enforce these rules. Two rules are Entity Integrity (Section 3.3.2) and Referential Integrity (Section 3.3.3). 3.4 Define the five basic relational algebra operations. Define the remaining three relational algebra operations in terms of the five basic operations. Five basic operations are: Selection and Projection (Unary) Cartesian Product, Union and Set Difference (Binary). There is also the Join, Intersection and Division operations: Can rewrite θ-join in terms of the basic selection and Cartesian product operations: R F S = σ F (R S) Can express the intersection operator in terms of the set difference operation: R S = R - (R - S) Can express the division operator in terms of the basic operations: T 1 = Π C (R) T 2 = Π C ( (S x T 1 ) - R) T = T 1 - T What is a view? Discuss the difference between a view and a base relation. Explain what happens when a user accesses a database through a view. View is the dynamic result of one or more relational operations operating on the base relations to produce another relation. Base relation exists as a set of data in the database. A view does not contain any data, rather a view is defined as a query on one or more base relations and a query on the view is translated into a query on the associated base relations. 8

9 Exercises The following tables form part of a database held in a relational DBMS:- Hotel Room Booking Guest (Hotel_No, Name, Address) (Room_No, Hotel_No, Type, Price) (Hotel_No, Guest_No, Date_From, Date_To, Room_No) (Guest_No, Name, Address) where and Hotel contains hotel details and Hotel_No is the primary key Room contains room details for each hotel and (Hotel_No, Room_No) forms the primary key Booking contains details of the bookings and the primary key comprises (Hotel_No, Guest_No, and Date_From) Guest contains guest details and Guest_No is the primary key. 3.6 Generate the relational algebra for the following queries: (a) List all hotels. HOTEL (b) List all single rooms with a price below 20 per night. σ type='s' AND price < 20 (ROOM) (c) List the names and addresses of all guests. Π name, address (GUEST) (d) List the price and type of all rooms at the Grosvenor Hotel. Π price, type (ROOM hotel_no (σ name='grosvenor Hotel' (HOTEL))) (e) List all guests currently staying at the Grosvenor Hotel. GUEST guest_no (σ date_from <= ' ' AND date_to >= ' ' ( BOOKING hotel_no (σ name='grosvenor Hotel' (HOTEL)))) (substitute ' ' for today s date). (f) List the details of all rooms at the Grosvenor Hotel, including the name of the guest staying in the room, if the room is occupied. (ROOM hotel_no (σ name='grosvenor Hotel' (HOTEL)) // Outer Join Π guest.name, hotel.hotel_no, room.room_no ( (GUEST guest_no (σ date_from <= ' ' AND date_to >= ' ' ( BOOKING hotel_no (σ name='grosvenor Hotel' (HOTEL)))) (substitute ' ' for today s date). (g) List the guest details (Guest_No, Name and Address) of all guests staying at the Grosvenor Hotel. Π guest_no, name, address (GUEST guest_no (σ date_from <= ' ' AND date_to >= ' ' ( BOOKING hotel_no (σ name='grosvenor Hotel' (HOTEL))))) (substitute ' ' for today s date). 9

10 3.7 Using relational algebra, create a view of all rooms in the Grosvenor Hotel, excluding price details. What would be the advantages of this view? Π room_no, hotel_no, type (ROOM hotel_no (σ name='grosvenor Hotel' (HOTEL))) Security - hides the price details from people who should not see it. Reduced complexity - a query against this view is simpler than a query against the two underlying base relations. 3.8 Produce the equivalent tuple and domain relational calculus statements for the above queries. Tuple Relational Calculus (a) (b) (c) (d) (e) (f) (g) RANGE OF H IS HOTEL {H} RANGE OF R IS ROOM {R R.Type = 'S' AND R.Price < 20} RANGE OF G IS GUEST {G.Name, G.Address} RANGE OF H IS HOTEL RANGE OF R IS ROOM {R.Price, R.Type H (R.Hotel_No = H.Hotel_No AND H.Name = 'Grosvenor Hotel')} RANGE OF H IS HOTEL RANGE OF G IS GUEST RANGE OF B IS BOOKING {G B ((B.Date_From <= ' ' AND B.Date_To >= ' ') AND (B.Guest_No = G.Guest_No) AND H (B.Hotel_No = H.Hotel_No AND H.Name = 'Grosvenor Hotel'))} Need to use Union of a relation containing all Rooms that are occupied with a relation extended by a NULL name for all unoccupied rooms. RANGE OF H IS HOTEL RANGE OF G IS GUEST RANGE OF B IS BOOKING {G.Guest_No, G.Name, G.Address B((B.Date_From <= ' ' AND B.Date_To >= ' ') AND (B.Guest_No = G.Guest_No) AND H (B.Hotel_No = H.Hotel_No AND H.Name = 'Grosvenor Hotel'))} Domain Relational Calculus (a) (b) (c) (d) {Hotel_No, Name, Address Hotel_No, Name, Address (HOTEL(Hotel_No, Name, Address)} {Room_No, Hotel_No, Type, Price Room_No, Hotel_No, Type, Price (ROOM(Room_No, Hotel_No, Type, Price) AND Type = 'S' AND Price < 20)} {Name, Address Name, Address (GUEST(Name, Address)} {Price, Type Room_No, Type, Price, Hotel_No 10

11 (ROOM(Hotel_No, Type, Price) AND Name (HOTEL(Hotel_No, Name) AND Name = 'Grosvenor Hotel')} (e) (f) {Guest_No, Guest.Name, Guest.Address Guest_No, Name, Address, (GUEST(Guest_No, Name, Address) AND Date_From, Date_To, Hotel_No (BOOKING(Hotel_No, Guest_No, Date_From, Date_To) AND Date_From <= ' ' AND Date_To >= ' ') AND Name (HOTEL(Hotel_No, Name) AND Name = 'Grosvenor Hotel')))} Rest similar to above. 3.9 Explain how the entity and referential integrity rules apply to these relations. For each relation, the primary key must not contain any nulls. Room is related to Hotel through the attribute Hotel_No. Therefore, the Hotel_No in Room should either be null or contain the number of an existing hotel in the Hotel relation. In this case study, it would probably be unacceptable to have a Hotel_No in Room with a null value. Booking is related to Hotel through the attribute Hotel_No. Therefore, the Hotel_No in Booking should either be null or contain the number of an existing hotel in the Hotel relation. However, because Hotel_No is also part of the primary key, a null value for this attribute would be unacceptable. Similarly for Guest_No. Booking is also related to Room through the attribute Room_No Analyze the RDBMSs that you are currently using. Determine the support the system provides for primary keys, alternate keys, foreign keys, relational integrity and views. What types of relational languages does the system provide? For each of the languages provided, what are the equivalent operations for the eight relational algebra operations? This is a small student project, the result of which is dependent on the system analyzed. 11

12 Review Questions Chapter 4 Database Planning, Design, and Administration 4.1 Discuss the relationship between the information system lifecycle and the database application lifecycle. See Sections 4.1 and Describe the purpose of each of the stage of the database application lifecycle. See Section Identify some of the techniques available to help document the users' requirements specification. See Section Describe the main aims of the conceptual and logical database design phases. The aims of conceptual database design are described in Section and the aims of logical database design are described in Section Explain why it is necessary to select the target database management system before commencing with the physical database design phase. Describe the main aims of physical database design. Physical database design is tailored to a specific DBMS, therefore it is essential the DBMS is determined before the physical design phase can begin. The aims of physical database design are described in Section Describe the prototype approach and identify the potential advantages of using this approach. See Section Outline the procedure for selecting a DBMS. See Section Define the purpose and tasks associated with data administration and database administration. Exercises See Section Produce a corporate data model for the Wellmeadows Hospital case study described in Appendix A. 12

13 Hospital Supplies Patient Management Doctor M 1 Refers M Item 1 M M 1 1 Drug Form Medication Takes Patient 1 Has M RelatedT Clinic NOK d GoesT 1 Attend 1 1 Is M M M Provides N Supplier Supply OPClinic Appointmt InPatient M 1 M M M M M WorksIn Examine AssignedTo Requires I For M 1 M 1 1 M M N Requisitio Makes Staff WorksIn Ward Has Bed M Receives Assume that you are responsible for selecting a new DBMS product for a group of users in your organization. To undertake this exercise, you must first establish a set of requirements Ward Management for the group and then identify a set of features that a DBMS product must provide to fulfill the requirements. Describe the process of evaluating and selecting the best DBMS product. The student should follow the approach to DBMS selection described in Section 4.6 and produce a report that identifies a suitable DBMS product that meets the requirements of the organization. The selection should be fully justified Assume that you are responsible for selecting a DBMS product for the Wellmeadows Hospital case study. Describe the process of evaluating and selecting the best DBMS product. The student should follow the approach to DBMS selection described in Section 4.6 and produce a report that identifies a suitable DBMS product that meets the requirements of the Wellmeadows Hospital case study. The selection should be fully justified and any assumptions made about the case study should be highlighted Investigate whether data administration and database administration exists as distinct functional areas within your organization. If identified, describe the organization, responsibilities, and tasks associated with each functional area. The student should investigate the organization and identify whether data administration and database administration exists as distinct functional areas. However, the student should be careful to note that these functions may be named differently, merged as a single function or included as part of a larger IT/IS function. If identified, the student should compile a report documenting the organization, responsibilities, and tasks. 13

14 Review Questions Part Two Methodology Chapter 5 Entity-Relationship Modeling 5.1 Describe the purpose of high-level data models in database design. The main purpose for developing a high-level data model is to support a user s perception of data and to conceal the more technical aspects associated with database design. Furthermore, a conceptual data model is independent of the particular DBMS and hardware platform that is used to implement the database. 5.2 Describe the basic concepts of the Entity-Relationship (ER) model. Present the diagrammatic representation of these concepts. The basic concepts of the Entity-Relationship model include entity types, relationship types, and attributes. See Section Describe the constraints that may be placed on participating entities in a relationship. There are two main types of restrictions on relationships called cardinality and participation constraints. See Section Describe the problems that may occur when creating an ER model. Problems may occur due to the misinterpretation of the meaning of certain relationships and these problems are referred to as connection traps. There are two main types of connection traps called fan traps and chasm traps. See Section Describe the main concepts associated with the Enhanced Entity-Relationship model. Present the diagrammatic representation of these concepts. Exercises The main concepts of the EER model are specialization/generalization, aggregation and categorization. However, in the accompanying textbook, we focus only on specialization/ generalization and categorization, which is associated with the related concepts of entity types described as superclasses or subclasses and the process of attribute inheritance. See Section 5.4 The University Accommodation Office Case Study The Director of the University Accommodation Office requires you to design a database to assist with the administration of the office. The requirements collection and analysis phase of the database design process based on the Director s view has provided the following requirements specification for the Accommodation Office database. (1) The data stored on each full-time student includes the matriculation number, name (first and last name), home address (street, city/town, postcode), date of birth, sex, category of student (for example, first year undergraduate (1UG), postgraduate (PG)), nationality, smoker (yes or no), special needs, any additional comments, current status (placed/waiting), and what course the student is studying on. The student information stored relates to those currently renting a room 14

15 and those on the waiting list. Students may rent a room in a university owned hall of residence or student flat. When a student joins the University he or she is assigned to a member of staff who acts as his or her Advisor of Studies. The Advisor of Studies is responsible for monitoring the student s welfare and academic progress. The data held on a student s Advisor includes their full name, position, name of department, internal telephone number, and room number. (2) Each hall of residence has a name, address, telephone number, and a hall manager who supervises the operation of the hall. The halls provide only single rooms, which have a room number, place number, and monthly rent rate. The place number uniquely identifies each room in all the halls controlled by the Accommodation Office and is used when renting a room to a student. (3) The Accommodation Office also offers student flats. These flats are fully furnished and provide single room accommodation for groups of 3, 4, or 5 students. The information held on student flats includes a flat number, address, and the number of single bedrooms available in each flat. The flat number uniquely identifies each flat. Each bedroom in a flat has a monthly rent rate, a room number, and a place number. The place number uniquely identifies each room available in all student flats and is used when renting a room to a student. (4) A student may rent a room in a hall or student flat for various periods of time. New lease agreements are negotiated at the start of each academic year with a minimum rental period of one semester (15 weeks) and a maximum rental period of one year, which includes Semesters 1, 2, and the Summer Semester. Each individual lease agreement between a student and the Accommodation Office is uniquely identified using a lease number. The data stored on each lease includes the lease number, duration of the lease (given as semesters), name, and matriculation number of the student, place number, room number, address details of the hall or student flat, the date the student wishes to enter the room, and the date the student wishes to leave the room (if known). (5) Student flats are inspected by staff on a regular basis to ensure that the accommodation is well maintained. The information recorded for each inspection is the name of the member of staff who carried out the inspection, the date of inspection, an indication of whether the property was found to be in a satisfactory condition (yes or no), and any additional comments. (6) Some information is also held on members of staff on the Accommodation Office and includes the staff number, name (first and last name), home address (street, city/town, postcode), date of birth, sex, position (for example, Hall Manager, Administrative Assistant, Cleaner), and location (for example, Accommodation Office or Hall). (7) The Accommodation Office also stores a limited amount of information on the courses run by the University including the course number, course title (including year), course leader s name, internal telephone number, and room number, and department name. Each student is associated with a single course. (8) Whenever possible, information on a student s next-of-kin is stored which includes the name, relationship, address (street, city/town, postcode), and contact telephone number. 5.6 Create an Enhanced Entity Relationship (EER) model to represent the data requirements of the University Accommodation Office case study. Develop the model using the following the steps: (a) Identify entity types. (b) Identify relationship types and determine the cardinality and participation constraints of the relationships. (c) Identify attributes and associate attributes with entity or relationship types. (d) Determine candidate and primary key attributes. (e) Specialize / generalize entity types (where appropriate). (f) Categorize entity types (where appropriate). (g) Draw the EER diagram. State any assumptions you made when creating the EER model. An example of a possible ER model for the University Accommodation Office case study is shown below. 15

16 Accomm adatio 1 M 1 Provid Room Fo M Lease Lease HallN d FlatN Place M Reques 1 Manag Hall 1 Works Flat 1 O M Inspecti IDat NOK 1 1 Advis Related M 1 Studen M Studi Matric 1 M M 1 1 Accom Staff StaffN 1 M Located Undertak 1 AcdStaff Office Academi Staff 1 Run M Cours Course The student should identify any ambiguities in the specification for the University Accommodation Office and state clearly his or her assumptions. For example, we may assume that we only hold information on a single next-of-kin per student and that some students do not provide this information. 16

17 Review Questions 6.1 Describe the purpose of normalizing data. Chapter 6 Normalization When we design a database for a relational system, the main objective in developing a logical data model is to create an accurate representation of the data, its relationships and constraints. To achieve this objective, we must identify a suitable set of relations. A technique that we can use to help identify such relations is called normalization. Normalization is a technique for producing a set of relations with desirable properties, given the data requirements of an enterprise. Normalization supports database designers by presenting a series of tests, which can be applied to individual relations so that a relational schema can be normalized to a specific form to prevent the possible occurrence of update anomalies. See also Sections 6.1 and Describe the problems that are associated with redundant data. A major aim of relational database design is to group attributes into relations so as to minimize information redundancy and thereby reduce the file storage space required by the base relations. Another serious difficulty using relations that have redundant information is the problem of update anomalies. These can be classified as insertion, deletion, or modification anomalies. See Section Describe the concept of functional dependency. Functional dependency describes the relationship between attributes in a relation. For example, if A and B are attributes of relation R, B is functionally dependent on A (denoted A B), if each value of A in R is associated with exactly one value of B in R. Functional dependency is a property of the meaning or semantics of the attributes in a relation. The semantics indicate how the attributes relate to one another and specify the functional dependencies between attributes. When a functional dependency is present, the dependency is specified as a constraint between the attributes. See also Section How is the concept of functional dependency associated with the process of normalization? Normalization is a formal technique for analyzing relations based on their primary key (or candidate keys in the case of BCNF) and functional dependencies. Normalization is often performed as a series of tests on a relation to determine whether it satisfies or violates the requirements of a given normal form. Three normal forms were initially proposed, which are called first (1NF), second (2NF) and third (3NF) normal form. Subsequently, a stronger definition of third normal form was introduced and is referred to as Boyce-Codd normal form (BCNF). All of these normal forms are based on the functional dependencies among the attributes of a relation. 6.5 Provide a definition for first, second, third and Boyce-Codd normal forms. First Normal Form (1NF) is a relation in which the intersection of each row and column contains one and only one value. Second Normal Form (2NF) is a relation that is in first normal form and every non-primary-key attribute is fully functionally dependent on the primary key. Third Normal Form (3NF) is a relation that is in first and second normal form in which no nonprimary-key attribute is transitively dependent on the primary key. 17

18 Boyce-Codd Normal Form (BCNF) is a relation in which every determinant is a candidate key. See also Sections 6.5 to Describe the purpose of fourth (4NF) and fifth (5NF) normal form. For 4NF see Section 6.11 and for 5NF see Section Exercises The table shown in Figure 6.25 lists dentist/patient appointment data. A patient is given an appointment at a specific time and date with a dentist located at a particular surgery. On each day of patient appointments, a dentist is allocated to a specific surgery for that day. StaffNo DentistName PatNo PatName Appointment Date Time SurgeryNo S1011 Tony Smith P100 Gillian White 12/9/ S15 S1011 Tony Smith P105 Jill Bell 12/9/ S15 S1024 Helen Pearson P108 Ian MacKay 12/9/ S10 S1024 Helen Pearson P108 Ian MacKay 14/9/ S10 S1032 Robin Plevin P105 Jill Bell 14/9/ S15 S1032 Robin Plevin P110 John Walker 15/9/ S13 Figure 6.25: Lists Dentist/Patient Appointment Data. 6.7 The table shown in Figure 6.25 is susceptible to update anomalies. Provide examples of insertion, deletion, and update anomalies. The student should provide examples of insertion, deletion and update anomalies using the data shown in the table. An example of a deletion anomaly is if we delete the details of the dentist called 'Helen Pearson', we also lose the appointment details of the patient called 'Ian MacKay'. 6.7 Describe and illustrate the process of normalizing the table shown in Figure 6.25 to Boyce-Codd normal forms. State any assumptions you make about the data shown in this table. The student should state any assumptions made about the data shown in the table. For example, we may assume that a patient is registered at only one surgery. Also, a patient may have more than one appointment on a given day. 18

19 1NF PK StaffNo ADate ATime DName PatNo PName SurgeryNo fd1 fd2 fd3 fd4 fd5 fd2 and fd4 violates 2NF 2NF StaffNo ADate ATime PatNo PName StaffNo ADate SurgeryNo StaffNo DName Fd3 violates 3NF 3NF / BCNF FK PK FK PK StaffNo ADate ATime PatNo StaffNo DName fd1 fd2 fd5 FK PK PK StaffNo ADate SurgeryNo PatNo PName fd4 Fd3 19

20 An agency called Instant Cover supplies part-time/temporary staff to hotels within Strathclyde Region. The table shown in Figure 6.26 lists the time spent by agency staff working at various hotels. The National Insurance Number (NIN) is unique for every member of staff. NIN ContractNo Hours EName H_No H_Loc 1135 C Smith J H25 East Kilbride 1057 C Hocine D H25 East Kilbride 1068 C White T H4 Glasgow 1135 C Smith J H4 Glasgow Figure 6.26: Instant Cover s Contracts. 6.8 The table shown in Figure 6.26 is susceptible to update anomalies. Provide examples of insertion, deletion, and update anomalies. The student should provide examples of insertion, deletion and update anomalies using the data shown in the table. An example of an update anomaly is if we wish to change the name of the employee called 'Smith J', we may only change the entry in the first row and not the last with the result that the database becomes inconsistent. 6.9 Describe and illustrate the process of normalizing the table shown in Figure 6.26 to Boyce-Codd Normal Form. State any assumptions you make about the data shown in this table. The student should state any assumptions made about the data shown in the table. For example, we may assume that a hotel may be associated with one or more contracts. 20

21 1NF PK NIN Contract_No Hours EName H_No H_Loc fd1 fd2 fd3 fd4 fd2 and fd3 violates 2NF 2NF NIN Contract_No Hours Contract_No H_No H_Loc NIN EName fd4 violates 3NF 3NF / BCNF FK FK PK PK FK NIN Contract_No Hours Contract_No H_No fd1 fd3 PK PK NIN EName H_No H_ Loc fd2 fd4 21

22 Review Questions Chapter 7 Methodology - Conceptual Database Design 7.1 Describe the purpose of a design methodology. A structured approach that uses procedures, techniques, tools, and documentation aids, to support and facilitate the process of design. A design methodology consists of phases that contain steps, which guide the designer in the choice of techniques that are appropriate at each stage of the project and also helps to plan, manage, control and evaluate database development projects. Furthermore, it is a structured approach for analyzing and modeling a set of requirements for a database in a standardized and organized manner. See Section Describe the main phases involved database design. See Section Identify important factors in the success of logical database design. See Section Discuss the important role played by users in the process of database design. The users' involvement throughout the database design phase is critical to providing the 'correct' system. In particular, the user should clarify any ambiguities in the specification that describes the required system and also review continually the development of the database design. The process of developing the database design is repeated until the user is prepared to 'sign-off' the design as being a 'true' representation of the part of the enterprise that is being modeling. See Sections and Describe the main objective of conceptual database design. See Section 7.3 Step Describe what a user view represents and the approaches that may be used to identify user views. User views can be identified using various methods. First, by examining the data flow diagrams that should have been produced previously to identify functional areas and possibly individual functions. Alternatively, by interviewing users, examining procedures, reports, forms, and/or observing the enterprise in operation. See also Section Identify the main tasks associated with conceptual database design. See Section Discuss the purpose of specialization/generalization of entity types, and discuss why this is an optional step in conceptual database design. See Section 7.3 Step Identify and describe the purpose of the documentation generated during conceptual database design. See Section 7.3 and in particular note the documentation generated at the end of each step. 22

23 Review Questions Chapter 8 Methodology - Logical Database Design for Relational Model 8.1 Identify the three main phases of database design and discuss the purpose of logical database design. The three main phases of database design are conceptual, logical, and physical. For purpose of logical database design see Section Describe the steps involved in refining a conceptual data model into a logical data model. See Section 8.1 Step Describe the rules for deriving relations that represent strong entity types, weak entity types, one-to-one binary relationship types, one-to-many relationship types, multi-valued attributes, and superclass/subclass relationships. See Section 8.1 Step Discuss how the technique of normalization can be used to validate the logical data model and the relations derived from the model. The logical data model can be validated using the technique of nomalization and against the transactions that the model is required to support. Normalization is used to improve the model so that it satisfies various constraints that avoid unnecessary duplication of data. Normalization ensures that the resultant model is a closer model of the enterprise that it serves, it is consistent, and has minimal redundancy and maximum stability. See also Section 8.1 Step Discuss two approaches that can be used to validate that the logical data model is capable of supporting the transactions required by the user s view. Two possible approaches to ensure that the logical data model supports the required transactions include: checking that all the information (entities, relationships and their attributes) required by each transaction is provided by the model in documenting a description of each transaction s requirements, and diagrammatically representing the pathway taken by each transaction directly on the ER diagram. See also Section 8.1 Step Describe the purpose of integrity constraints and identify the five main types of constraints. The main types of constraints include: There are five types of integrity constraints: required data, attribute domain constraints, entity integrity, referential integrity, and enterprise constraints. See also Section 8.1 Step Describe the alternative strategies that can be applied if there exists a child occurrence referencing a parent occurrence that we wish to delete. There are several strategies to consider when there exists a child occurrence referencing the parent occurrence that we are attempting to delete: NO ACTION, CASCADE, SET NULL, SET DEFAULT, and NO CHECK. See also Section 8.1 Step Identify the tasks typically associated with merging local logical data models into a global logical model. 23

24 See Section 8.1 Step 3 and in particular Step

25 Review Questions Chapter 9 Methodology - Physical Database Design for Relational DBMSs 9.1 Explain the difference between logical and physical database design. Why might these tasks be carried out by different people? Logical database design is concerned with building the data model for the organization that is completely independent of any DBMS. Physical database design, however, is concerned with actually defining the data model using the DDL of a particular DBMS. Consequently, logical database design focuses on what the data model represents, whereas physical database design focuses on how the data model is to be implemented. Different skills are required to undertake these design phases, which are often found in different people. See Section Describe the inputs and outputs of physical database design. The inputs are the global logical data model and the data dictionary. The outputs are the base relations, integrity rules, file organization specified, secondary indexes determined, user views and access rules. See Section Describe the purpose of the main steps in the physical design methodology presented in this chapter. Step 4 Step 5 Step 6 Step 7 Produces a relational database schema from the global logical data model. This includes integrity rules. Determines the file organizations for the base relations. This takes account of the nature of the transactions to be carried out, which also determine where secondary indexes will be of use. As a result of analyzing the transactions, the design may be altered by incorporating controlled redundancy into it. Designs the security measures for the database implementation. This includes designing the user views and the access rules on the relations and views. Monitors the database application systems and improves performance by making amendments to the design as appropriate. See also Section "One of the main objectives of physical database design is to store data in an efficient way." How might we measure efficiency in this context? This can be measured by the number of transactions that can be processed by the system in a given time frame, or by the length of time it takes to complete one transaction, or by the amount of disk storage taken up by the database files. See also Section 9.3 Step Under what circumstances would we want to denormalize a logical data model? Use examples to illustrate your answer. Generally, if overall performance needs to be improved, controlled redundancy can be introduced. See also Section 9.3 Step 5.4. Examples: If queries on staff always required the branch address, this attribute could be posted into staff. The effect on updating would be minimal if branch data was relatively static, and it removes a join from the query. 25

26 If the number of staff for each branch was often required with branch details, a derived attribute could be placed in branch. This would remove the need to access and repeatedly count the relevant records in staff. When staff joined or left a branch, this attribute would required updating. 26

27 Exercises Chapter 10 Conceptual Database Design Methodology - Worked Example The Wellmeadows Hospital case study 10.1 Identify user views for the Medical Director and Charge Nurse in the Wellmeadows Hospital case study, described in Appendix A. See Appendix A 10.2 List the users' requirements specification for each of these views. The student should examine the case study in detail and identify and compile a user specification for the Medical Director s and the Charge Nurse s views. As an additional task the student may also compile a specification for the Personnel Officer s view. Of course to complete this exercise will require that the student makes some ascertions about the precise requirements of each user view. Any assumption should be documented along with each view. Examples of specification for the Medical Director s and Charge Nurse s views are shown below. Medical Director The Director is responsible for the overall management of the hospital and must maintain control over the use of resources (including staff, beds, and supplies) in the provision of cost-effective treatment for all patients. 1. The hospital is composed of many wards. Each ward is managed by a Charge Nurse. The information to be held on each ward includes the ward name, number (e.g. W1), phone number, location (e.g. Block E), number of beds and the name of the Charge Nurse. 2. Each ward is allocated staff including (e.g. Charge nurse, senior and junior nurses, doctors, consultants, auxiliaries). 3. The hospital maintains a central stock of surgical (e.g. syringe, bandages) and nonsurgical (e.g. plastic bags, aprons). The details of surgical and non-surgical supplies includes item number and name, item description, quantity in stock, re-order level, cost per unit. The supplies used by each ward is monitored. The hospital also maintains a stock of pharmaceutical supplies (e.g. antibiotics, pain killers). The details of pharmaceutical supplies includes drug number and name, description, dosage, quantity in stock, re-order level, cost per unit. The pharmaceutical supplies used by each ward is monitored. 4. The details of the suppliers of the surgical, non-surgical and pharmaceutical items are stored. The information stored includes the supplier name and number, address, phone and fax number. 5. Patients are normally referred to the hospital for treatment by their local doctor. The details of local doctors are stored including the their name, clinic number, address and phone number. 6. The details of patients referred to the hospital includes the patient number, name (first and last name), address, phone number, date of birth, martial status, next-of-kin details (name, relationship, address and phone number). 27

28 7. When a patient is referred by their doctor to attend the hospital, the patient is given an appointment and is examined by a consultant. The details of the appointment are stored including the consultant s name and number, appointment number, date, time and examination room (e.g. Room E112). As a result of the examination, the patient is either recommended to attend the outpatient clinic or placed on a waiting list until a bed can be found in a particular ward. 8. The details of outpatients are stored. The information stored includes the patient details as stated earlier (see 6) and the date and time of the appointment at the outpatient clinic. 9. The details of patients currently placed in a ward and those on the waiting list for a place on a ward are stored. The information stored includes the patient details as stated earlier (see 6) and the date placed on waiting list, ward required, expected duration of stay, date placed in the ward and date left the ward. Charge Nurse The Charge Nurse has overall responsibility for the management of a single ward. The Charge Nurse is allocated a budget to run the ward and must ensure that all resources (staff, beds and supplies) are used effectively in the care of patients. The Charge Nurse and other senior medical staff are responsible for the allocation of beds to patients on the waiting list. 1. The information to be held on each ward includes the details of staff allocated to each ward including the staff number, name, address, phone number, position, number of hours worked per week and shift (e.g. early, late). 2. The information stored on each patient on the waiting list includes the patient number, name (first and last name), address, phone number, date of birth, martial status, next-ofkin details, date placed on waiting list, required ward, date placed in ward, expected duration of stay, date left ward. 3. When a patient enters the ward they are allocated a bed with a unique bed number. Each patient is prescribed medication and the details of this medication includes the patient number, drug number and name, units per day, start and finish date. The medication (pharmaceutical supplies) given to each patient is monitored. 4. Staff are allocated to work in wards, as required. The Charge Nurse of each ward is responsible for creating a staff rota which ensures that the correct complement of staff are on duty for each shift (early, late, night). Nursing staff may be specifically allocated to patients who required specialist care. 5. When required the Charge Nurse may obtain surgical, non-surgical and pharmaceutical supplies from the central stock of supplies held by the hospital. The information to be stored includes the requisition number, staff name and number, ward number, item number (or drug number), quantity required, date ordered and date received Create local conceptual data models for each of the user views. State any assumptions necessary to support your design. The student should create local conceptual data models using the requirements specification for the Medical Director and the Charge Nurse. This should include an ER model representing each user view and the supporting documentation that describes the models. Throughout the process of design, the student should clearly state any assumptions necessary to support his or her design. 28