CMP-3440 Database Systems

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1 CMP-3440 Database Systems Database Architecture Lecture 02 zain 1

2 Database Design Process Application 1 Conceptual requirements Application 1 External Model Application 2 Application 3 Application 4 External Model External Model External Model Application 2 Conceptual requirements Application 3 Conceptual requirements Conceptual Model Logical Model Internal Model Application 4 Conceptual requirements 2

3 Three-Level Architecture External Level Users view of the database. Describes that part of database that is relevant to a particular user Conceptual Level Community view of the database. Describes what data is stored in database and relationships among the data. Internal Level Physical representation of the database on the computer. Describes how the data is stored in the database. 3

4 Stages in Database Design 1. Requirements formulation and analysis 2. Conceptual Design -- Conceptual Model 3. Implementation Design -- Logical Model 4. Physical Design --Physical Model 4

5 Stages in Database Design 1. Requirements formulation and analysis Purpose: Identify and describe the data that are used by the organization Results: Metadata identified, Data Dictionary, Conceptual Model-- ER diagram 5

6 Stages in Database Design 1. Requirements formulation and analysis Systems Analysis Process Examine all of the information sources used in existing applications Identify the characteristics of each data element numeric text date/time etc. Examine the tasks carried out using the information Examine results or reports created using the information 6

7 Stages in Database Design 2. Conceptual Model Merge the collective needs of all applications Determine what Entities are being used Some object about which information is to maintained What are the Attributes of those entities? Properties or characteristics of the entity What attributes uniquely identify the entity What are the Relationships between entities How the entities interact with each other? 7

8 Stages in Database Design 3. Physical (Internal) Model Choices of index file structure Choices of data storage formats Choices of disk layout 8

9 Stages in Database Design External Model User views of the integrated database Making the old (or updated) applications work with the new database design 9

10 Developing a Conceptual Model Elements of the Conceptual Model are represented by diagrams, Entity-Relationship or ER Diagrams Entity is an object in the real world (or even imaginary worlds) about which we want or need to maintain information Persons (e.g.: customers in a business, employees, authors) Things (e.g.: purchase orders, meetings, parts, companies) Employee 10

11 Entities Strong VS Weak Entities: Weak entities owe existence entirely to another entity while strong entities are not existence dependent. Order Order-line 11

12 Attributes Attributes are the significant properties or characteristics of an entity that help identify it and provide the information needed to interact with it or use it. (This is the Metadata for the entities.) Birthdate First Age Middle Name Employee SSN Last Projects 12

13 Types of Attributes Simple: Each entity has a single atomic value for the attribute, for example SSN, CourseNo. Composite: The attribute may be composed of several components Multivalued: An entity may have multiple values for that attribute; for example Color of a Car or PreviousDegrees of a Student Derived: The domain value of attribute can be determined from one or more other attributes. 13

14 Developing a Conceptual Model Relationships are the associations between entities. They can involve one or more entities and belong to particular relationship types One to One Student Class One to Many Project Supplier Part 14

15 Developing a Conceptual Model Many to Many Relationships Project Assignment Project Employee

16 Associations Unary or Recursive Relationships Person Is-married-to Employee manages manager

17 Associations Binary Relationships Employee Is-assigned One-to-one Parking Place Product Line contains One-to-many Product Student Registers-for Many-to-many Course

18 Associations Ternary Relationships Part Vendor Warehouse

19 Derived Attributed Student name ssn dateofbirth /age Registers-for Derived attribute Course Offering term section time location Scheduled-for Course crsecode crsetitle credithrs /participant Derived role {age = currentdate dateofbirth} /Takes Derived association

20 Enhanced Entity-Relationship Model EERM also useful to represent many real-world objects that can be classified naturally into hierarchies. Additional concepts of EER model includes Specialization / Generalization, & categorisation.

21 Concepts of Generalization / Specialization Superclass it is an entity type it is at a high level (Generalisation) It includes distinct subclasses that require to be represented in a data model. it is also known as a Supertype

22 Concepts of Generalization / Specialization Subclass it is an entity type it is at a lower level (Specialisation) it is a subset of a supertype it has a distinct role it is also known as a subtype the relationship with a superclass represents an IS-A relationship it shares common attributes or relationships distinct from other subsets

23 Concepts of Generalization / Specialization Generalization Process The process of minimising the differences between entities by identifying their common features. There are 4 combinations of Specialization & generalization hierarchy Disjoint Mandatory Disjoint Optional Overlapping Optional Overlapping Mandatory

24 Generalization Employee empname empnumber address datehired printlabel() Hourly Employee HourlyRate computewages() Salaried Employee Annual Sal stockoption Contributepension() Consultant contractnumber billingrate computefees()

25 Super key Candidate key Primary key Foreign key Alternate keys Relational Keys

26 ER Notations: Crow 26

27 ER Notations: Chen 27

28 Integrity Constraints Entity Integrity primary key attribute cannot be null Referential Integrity foreign key value must always match a candidate key value in its home relation or foreign key value must be wholly null

Modeling Databases Using UML

Modeling Databases Using UML Fall 2017, Lecture 4 There is nothing worse than a sharp image of a fuzzy concept. Ansel Adams 1 Software to be used in this Chapter Star UML http://www.mysql.com/products/workbench/