1. Considering functional dependency, one in which removal from some attributes must affect dependency is called

Size: px

Start display at page:

Download "1. Considering functional dependency, one in which removal from some attributes must affect dependency is called"

Aubrie Porter
5 years ago
Views:

1 Q.1 Short Questions Marks 1. Considering functional dependency, one in which removal from some attributes must affect dependency is called 01 A. full functional dependency B. partial dependency C. prime functional dependency D. transitive dependency Ans: A. full functional dependency 2. Define: Instance and Schema. 01 Instance: The data stored in database at a particular moment of time is called instance of database. It is also called database state or snapshot. Schema: The description of a database is called the database schema, which is specified during database design and is not expected to change frequently. 3. List out the Mapping Cardinalities in ER diagram 01 i. One to one ii. One to many iii. Many to one iv. Many to many 4. can be used to retrieve data from multiple tables. 01 A. Embedded SQL. B. Dynamic C. Joins. D. Views. Ans: Joins 5. is an attribute, or set of attributes, that uniquely identifies a tuple within a relation 01 A. Foreign key B. Super key C. Matching Key D. None of above Ans: B. Super key 6. Define DBMS 01 Database management system (DBMS): is a collection of programs that enables users to create and maintain a database. The DBMS is hence a general-purpose software system that facilitates the processes of defining,

2 constructing, manipulating, and sharing databases among various users and applications. Q.2 (a) Explain generalization and specialization with suitable example. 03 Specialization Specialization is the process of defining a set of subclasses of an entity type; this entity type is called the superclass of the specialization. The set of subclasses that forms a specialization is defined on the basis of some distinguishing characteristic of the entities in the superclass. For example, the set of subclasses {SECRETARY,ENGINEER, TECHNICIAN} is a Specialization of the superclass EMPLOYEE that distinguishes among employee entities based on the job type of each employee entity. Attributes that apply only to entities of a particular subclass such as TypingSpeed of SECRETARY are attached to the rectangle representing that subclass. These are called specific attributes (or local attributes) of the subclass. Similarly, a subclass can participate in specific relationship types, such as the HOURLY_EMPLOYEE subclass participating in the BELONGS_TO relationship

3 Generalization The reverse process of abstraction in which we suppress the differences among several entity types, Identify their common features, And generalize them into a single superclass of which the original entity types are special subclasses. We can view {CAR, TRUCK} as a specialization of VEHICLE, rather than viewing VEHICLE as a generalization of CAR and TRUCK. Similarly, in Figure 8.1 we can view EMPLOYEE as a generalization of SECRETARY, TECHNICIAN, and ENGINEER. (b) Explain the three level architecture of DBMS. 04

4 In this architecture, schemas can be defined at the following three levels: 1. The internal level has an internal schema, which describes the physical storage structure of the database. It also describes the data type of the data items, the size of the items in the storage media, the location of the data items etc. The internal schema uses a physical data model and describes the complete details of data storage and access paths for the database. 2. The conceptual level has a conceptual schema, which describes the structure of the whole database for a community of users. The conceptual schema hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints. Usually, a representational data model is used to describe the conceptual schema when a database system is implemented. 3. The external or view level includes a number of external schemas or user views. Each external schema describes the part of the database that a particular user group is interested in and hides the rest of the database from that user group. As in the previous case, each external schema is typically implemented using a representational data model, possibly based on an external schema design in a highlevel data model. The processes of transforming requests and results between levels are called mappings. These mappings may be time-consuming, so some DBMSs-especially those that are meant to support small databases-do not support external views. Even in such systems, however, a certain amount of mapping is necessary to transform requests between the conceptual and internal levels. (c) 05 Solve the queries for the following database using Relational Algebra branch (branch-name, branch-city, assets) customer (customer-name, customer-street, customer-only) account (account-number, branch-name, balance) loan (loan-number, branch-name, amount) depositor (customer-name, account-number) borrower (customer-name, loan-number)

5 1. Find all loans of over $1200 σamount > 1200 (loan) 2. Find the loan number for each loan of an amount greater than $1200 loan-number (σamount > 1200 (loan)) 3. Find the names of all customers who have a loan, an account, or both, from the bank customer-name (borrower) customer-name (depositor) 4. Find the names of all customers who have a loan and an account at bank. customer-name (borrower) customer-name (depositor) 5. Find the names of all customers who have a loan at the Perryridge branch. customer-name (σbranch-name= Perryridge (σborrower.loan-number = loan.loannumber(borrower x loan))) OR (c) 05 Define E-R diagram. Draw an E-R diagram for Library Management System. Assume relevant entities and attributes for the given system. E-R Diagram: ER diagram is use to design the database for ER model. An Entity Relationship Diagram (ERD) is a visual representation of different data using conventions that describe how these data are related to each other. ER diagram have the following component 1) Entity 2) Attributes 3) Relationship

6 Library Management System Q.3 (a) Who is DBA? Explain the role of DBA in DBMS. 03 The DBA is responsible for authorizing access to the database, for coordinating and monitoring its use, and for acquiring software and hardware resources as needed. The Database Administrator, better known as DBA, is the person (or a group of persons) responsible for the well being of the database management system. It has the following functions and responsibilities regarding database management: 1. Definition of the schema, the architecture of the three levels of the data abstraction, data independence. 2. Modification of the defined schema as and when required. 3. Definition of the storage structure i.e. and access method of the data stored i.e. sequential, indexed or direct. 4. Creating new used-id, password etc, and also creating the access permissions that each user can or cannot enjoy. DBA is responsible to create user roles, which are collection of the permissions (like read, write etc.) granted and restricted for a class of users. She can also grant additional permissions to and/or revoke existing permissions from a user if need be.

7 5. Defining the integrity constraints for the database to ensure that the data entered conform to some rules, thereby increasing the reliability of data. 6. Creating a security mechanism to prevent unauthorized access, accidental or intentional handling of data that can cause security threat. 7. Creating backup and recovery policy. This is essential because in case of a failure the database must be able to revive itself to its complete functionality with no loss of data, as if the failure has never occurred. (b) What is a Join? Explain different types of outer join with appropriate example. Natural Join Natural Join Operation ( ) Operation: Natural join will retrieve information from multiple relations. It works in three steps. 1. It performs Cartesian product 2. Then it finds consistent tuples and inconsistent tuples are deleted 3. Then it deletes duplicate attributes Symbol: Notation: Relation1 Relation2 Consider following table The Outer Join Operation An outer join does not require each record in the two joined tables to have a matching record. In natural join some records are missing if we want that missing records than we have to use outer join. The outer join operation can be divided into three different forms: 1. Left outer join 2. Right outer join 3. Full outer join

Consider following tables Left outer join The left outer join retains all the tuples of the left relation even

For such kind of tuples having no matching, the attributes of right relation will be padded with null in

Right outer join The right outer join returns all the tuples of the right relation even though there is no

8 Consider following tables Left outer join The left outer join retains all the tuples of the left relation even through there is no matching tuple in the right relation. For such kind of tuples having no matching, the attributes of right relation will be padded with null in resultant relation. Right outer join The right outer join returns all the tuples of the right relation even though there is no matching tuple in the left relation. For such kind of tuples having no matching, the attributes of left relation will be padded with null in resultant relation. Full outer join Returns all the tuples of both of the relations. It also pads null values whenever required.

9 (c) What is Normalization? What are its characteristics? Explain 1NF and 2NF in detail 05 Normalization:: Normalization is a process to distribute a single table into multiple tables with specified relationship between tables and helps to avoid redundant data in table. Database normalization is the process of removing redundant data from your tables to improve storage efficiency, data integrity, and scalability. In the relational model, methods exist for quantifying how efficient a database is. These classifications are called normal forms (or NF), and there are algorithms for converting a given database between them. Normalization generally involves splitting existing tables into multiple ones, which must be re-joined or linked each time a query is issued. Characteristics Eliminates redundant data Reduces chances of data errors Reduces disk space Improve data integrity, scalability and data consistency. First Normal Form : It is also known as 1NF. A table is in 1 st normal form if There are no repeating groups All the key attributes are defined Assigning primary key to each table.

10 A relation R is in first normal form (1NF) if and only if all underlying domains contain atomic values only. OR A relation R is in first normal form (1NF) if and only if it does not contain any composite or multi valued attributes or their combinations. Example: Above relation has four attributes Cid, Name, Address, Contact_no. Here address is composite attribute which is further divided in to sub attributes as Society and City. Another attribute Contact_no is multi valued attribute which can store more than one values. So above relation is not in 1NF. Problem Suppose we want to find all customers for some particular city then it is difficult to retrieve. Reason is city name is combined with society name and stored whole as address. Solution Insert separate attribute for each sub attribute of composite attribute. Insert separate attribute for multi valued attribute and insert only one value on one attribute and other in other attribute. So above table can be created as follows.

11 Second Normal Form It is also known as 2NF. A table is in 2 nd normal form if It is in 1 st normal form and It includes no partial dependencies No partial dependencies means all non-key attributes are fully functionally dependent on the primary key. Definition. A relation schema R is in 2NF if every nonprime attribute A in R is fully functionally dependent on the primary key of R. A table is said to be in its second normal form when each record in the table is in the first normal form and each column in the record is fully dependent on its primary key. Example: Above relation has five attributes cid, ano, acess_date, balance, bname and two FDS FD1 {cid,ano} {acess_date,balance,bname} and FD2 ano {balance,bname} We have cid and ano as primary key. As per FD2 balace and bname are only depend on ano not cid. In above table balance and bname are not fully dependent on primary key but these attributes are partial dependent on primary key. So above relation is not in 2NF. Problem For example in case of joint account multiple customers have common accounts. If some account says A02 is jointly by two customers says C02 and C04 then data values for attributes balance and bname will be duplicated in two different tuples of customers C02 and C04.

12 Solution Decompose relation in such a way that resultant relation does not have any partial FD. For this purpose remove partial dependent attribute that violets 2NF from relation. Place them in separate new relation along with the prime attribute on which they are full dependent. The primary key of new relation will be the attribute on which it if fully dependent. Keep other attribute same as in that table with same primary key. So above table can be decomposed as per following. OR Q.3 (a) What is functional dependency? List the different types 03 Functional Dependency: Let R be a relation schema having n attributes A1, A2, A3,, An. Let attributes X and Y are two subsets of attributes of relation R. If the values of the X component of a tuple uniquely (or functionally) determine the values of the Y component, then, there is a functional dependency from X to Y. This is denoted by X Y. It is referred as: Y is functionally dependent on the X, or X functionally determines Y. The abbreviation for functional dependency is FD or fd. The set of attributes X is called the left hand side of the FD, and Y is called the right hand side. The left hand side of the FD is also referred as determinant whereas the right hand side of the FD is referred as dependent. Functional dependency preserves a formal mechanism for defining constraints among various attribute of a relation.

13 Types of Functional Dependencies i. Full Dependency ii. Partial Dependency iii. Transitive Dependency iv. Trivial FD: v. Nontrivial FD vi. Multivalued dependency vii. Join dependency (b) List the steps in proper sequence in order to convert an ER and EER diagram into tables. 04 STEPS Step 1: Mapping of Regular Entity Types. For each regular (strong) entity type E in the ER schema, create a relation R that includes all the simple attributes of E. Step 2: Mapping of Weak Entity Types. For each weak entity type W in the ER schema with owner entity type E, create a relation R and include all simple attributes of W as attributes of R. In addition, include as foreign key attributes of R the primary key attributes of the relations that correspond to the owner entity types Step 3: Mapping of Binary 1:1 Relationship Types. Identify the relations S and T that correspond to the entity types participating

14 in R.. Include a foreign key in T correspond to the primary key of the relation S that represents the other entity type participating in S Step 4: Mapping of Binary 1 :N Relationship Types. Identify the relation S that represents the participating entity type at the N- side of the relationship type. Include as foreign key in S the primary key of the relation T that represents the other entity type participating in R.(Dnumber-Dno, ssn-superssn) Step 5: Mapping of Binary M:N Relationship Types. Create a new relation S to represent R. Include as foreign key attributes in S the primary keys of the relations that represent the participating entity types. Step 6: Mapping of Multivalued Attributes. For each multivalued attribute A, create a new relation R. This relation R will include an attribute corresponding to A, plus the primary key attribute K as a foreign key in R of the relation that represents the entity type or relationship type that has A as an attribute. Step 7: Mapping of N-ary Relationship Types. For each n-ary relationship type R, where n > 2, create a new relation S to represent R. Include as foreign key attributes in S the primary keys of the relations that represent the participating entity types. Also include any simple attributes of the n-ary relationship type (or simple components of composite attributes) as attributes of S. (c) Draw an Entity Relation diagram for the Hospital Management System. Consider the different types of Patients with respect to Disease and In- Patient and Out-Patient Department in the design. Consider the availability of all well qualified Doctors. Consider various types of tests and operations to be conducted. Explain the mapping cardinality used. Assume suitable attributes. Use generalization and Specialization.

15 Mapping Cardinality used are explained below. a. Hospital has a set of patients. Therefore the relations is 1..N. b. Hospital has a set of doctors. Therefore the relations is 1..N. c. Doctor are associated with each patient. Therefore the relations is N..1. d. Each patient has record of various test and examination conducted. Therefore the relations is 1..N.

A database can be modeled as: + a collection of entities, + a set of relationships among entities.

A database can be modeled as: + a collection of entities, + a set of relationships among entities. The Relational Model Lecture 2 The Entity-Relationship Model and its Translation to the Relational Model Entity-Relationship (ER) Model + Entity Sets + Relationship Sets + Database Design Issues + Mapping