Data Modeling During System Analysis. Logical Data Model Stages. What is Conceptual Database Design? Gathering Information for Conceptual

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1 Data Modeling Entity Relationship Diagram Lecture 16 CSC(291) [Software Engineering 1] Instructor: Saif-ur-Rehman Khan COMSATS Institute of Information Technology, Islamabad Data Modeling During System Analysis Data models help analysts to quickly identify business vocabulary more completely than process models. Data models are almost always built more quickly than process models. A complete data model can fit on a single sheet of paper. Process models require dozens of sheets of paper. Process modelers frequently and too easily get hung up on unnecessary detail. Data models for existing and proposed systems are far more similar than process models for existing and proposed systems. Consequently, there is less work to throw away as you move into later phases. 2 Logical Data Model Stages 1. Construct the Context Data Model. 2. Next, a Key based Data Model will be drawn. 3. Next, a Fully Attributed Data Model will be constructed. 4. The completes data model is analyzed for adaptability and flexibility through a process called normalization. What is Conceptual Database Design? Process of describing the data, relationships between the data, and the constraints on the data. After analysis Gather all the essential data required and understand how the data are related. The focus is on the data, rather than on the processes. The output of the conceptual database design is a Conceptual Data Model ( + Data Dictionary). 3 4 Gathering Information for Conceptual Data Modeling Two perspectives Top down Data model is derived from an intimate understanding of the business. Bottom up Data model is derived by reviewing specifications and business documents. Introduction to E R Modeling The basic entity relationship modeling notation uses three main constructs: 1. Data entities, 2. Relationships, and 3. Their associated attributes. 5 6

2 E R Data Model E R is a detailed, logical representation of the data for an organization or for a business area. The E R model lis expressed in terms of entities ii in the business environment, the relationships or associations among those entities, and the attributes or properties of the entities and their relationships. E R Diagram An E R model is normally expressed as an Entity Relationship diagram (E R diagram), which is graphical representation of E R model. 7 8 Chen Notation Crow s Foot Notation Association between the instances of one or more entity types Entity Attribute Relationship EntityName Verb Phrase AttributeName EntityName EntityName Verb phrase List of Attributes Person, place, object, event or concept about which data is to be maintained named property or characteristic of an entity Represents a set or collection of objects in the real world that share the same properties Acceptable Entities An entity is a person, place, object, event, or concept in the user environment about which the organization wishes to maintain data. An entity has its own identity that distinguishes it from each other entity. E.g., Person: EMPLOYEE, STUDENT, PATIENT, AGENCY, DEPARTMENT, DIVISION, INSTRUCTOR, SUPPLIER Place: STORE, WAREHOSE, STATE, SALES REGION, BUILDING, ROOM, BRANCH OFFICE, CAMPUS Object: MACHINE, BUILDING, AUTOMOBILE, PRODUCT Event: SALE, REGISTRATION, RENEWAL, BOOK RESERVATION, CANCELLATION, ORDER, RESERVATION, SALE, TRIP Concept: ACCOUNT, COURSE, WORK CENTER, QUALIFICATION 11 Entities EMPLOYEE COURSE ACCOUNT 12

3 Naming and Defining Entity Types 1. An entity type name is a singular noun (such as CUSTOMER, STUDENT, or AUTOMOBILE). 2. An entity type name should be descriptive and specific to the organization. E.g., a PURCHASE ORDER for orders placed with us by our customers. Both of these entity types cannot be named ORDER. 2. An entity name should be concise, e.g., in a university database, using REGISTRATION for the event of student registering for a class rather than STUDENT REGISTARTION FOR CLASS. 3. Event entity types should be named for the result of the event, not the activity or process of the event. E.g., the event of a project manager assigning an employee to work on a project results in an ASSIGNMENT. Attributes A named property or characteristics of an entity that is of interest to the organization. STUDENT: Student_ID, Student_Name, Home_Address, Phone_Num,ber, Major AUTOMOBILE: Vehicle_ID, Color, Weight, Horsepower EMPLOYEE: Employee_ID, Employee_Name, Payrol_Address Composite Attributes Naming and Defining Attributes 1. An attribute name is a noun (such as Custome_ID, Age, or Prodcut_Minimum _Price) 2. An attribute name should be unique. 3. Each attribute should follow a standard format Relationships Relationships are the glue that hold together the various components of an E R model. Naming and Defining Relationships Relationships may be the most difficult component of an E R diagram to understand. STUDENT Registers for COURSE 1. A relationship name is a verb phrase (such as assigned_to, Supplies_to, or Teaches). 2. You should avoid vague names, (such as has or Isrelated_to)

Degree of Relationships Cardinality and Connectivity Degree: number of entity types that participate in a relationship Three cases

three entity types Relationships can be classified as either one to one one to many Connectivity many to many Cardinality : minimum

19 20 Cardinality and Connectivity Cardinality and Connectivity 1 M (1,4) (1,1) A professor class OR A class is taught by professor

4 Degree of Relationships Cardinality and Connectivity Degree: number of entity types that participate in a relationship Three cases Unary: between two instances of one entity type Binary: between the instances of two entity types Ternary: among the instances of three entity types Relationships can be classified as either one to one one to many Connectivity many to many Cardinality : minimum and maximum number of instances of Entity B that can (or must be) associated with each instance of entity A Cardinality and Connectivity Cardinality and Connectivity 1 M (1,4) (1,1) A professor class OR A class is taught by professor How Many?? (1,1) (1,4) Connectivity Chen Model 1 to represent one. M to represent many 1 M Crow s Foot One many Mandatory one, means (1,1) One or many 24

MS Access can generate ERD of Third Normal Form Example A university consists of a number of departments. Each department offers several courses. A number of modules make up each course.

Each module is taught by a lecturer from the appropriate department, and each lecturer tutors a group of students Find Entities and Relationships among entities.

5 MS Access can generate ERD of Third Normal Form Example A university consists of a number of departments. Each department offers several courses. A number of modules make up each course. Students enrol in a particular course and take modules towards the completion of that course. Each module is taught by a lecturer from the appropriate department, and each lecturer tutors a group of students Find Entities and Relationships among entities. Next draw an ERD of the above given scenario? 26 Example : Entities A university consists of a number of departments. Each department offers several courses. A number of modules make up each course. Students enrol in a particular course and take modulestowards the completion of that course. Each module is taught by a lecturer from the appropriate department, and each lecturer tutors a group of students Example : Relationships A university consists of a number of departments. Each department offers several courses. A number of modules make up each course. Students enrol in a particular course and take modulestowards the completion of that course. Each module is taught by a lecturer from the appropriate department, and each lecturer tutors a group of students Example : ER Diagram A Case Study Conference Centre Booking System A conference centre takes bookings from clients who wish to hold courses or conferences at the centre. When clients make bookings they specify how many people are included in the booking, and of these, how many will be resident during the booking, and how many will require catered or non-catered accommodation at the centre. The centre contains a number of facilities which may be required by clients making bookings as follows: A. There are 400 bedrooms for clients who will be resident during the Course or conference. B. A maximum of 250 catered people can be handled at any one time. C. Six main lecture theatres providing seating for 200 people. D. Twenty seminar rooms each able to accommodate 25 people. E. Video conference facilities. The video conference facilities consist of four separate video conference networks. Each video conference network has a large screen based in one of the main lecture theatres, along with 3 satellite screens each of which is based in one of the seminar rooms. 29 Draw an entity relationship diagram for the case, stating any assumptions you deem necessary.

6 References 1. Rogers S. Pressman. (2005). SOFTWARE ENGINEERING, A PRACTITIONER S APPROACH, (6 th Ed.), Chapter 8, Building the Analysis Model, pp db.stanford.edu/~ullman/fcdb.html

IS 263 Database Concepts

IS 263 Database Concepts Lecture 1: Database Design Instructor: Henry Kalisti 1 Department of Computer Science and Engineering The Entity-Relationship Model? 2 Introduction to Data Modeling Semantic data