Basic Concepts of Databases

1. Basic Concepts of Databases CST203-2 Database Management Systems Lecture 2

2. One Tier Architecture • Eg: • In this scenario, a workgroup database is stored in a shared location on a single machine • Beneficial when we are dealing with data that is relevant to a single user

3. Client / Server architecture System functionality is distributed between • Client module • Server module

4. 3 tier architecture • To ensure more security and load balancing for a greater stability

5. Data models • A collection of concepts that can be used to describe the structure of a database • “An integrated collection of concepts for describing data, relationships between data, and constraints on the data. • Database Solutions: A Step-by-step approach to building databases • Include a set of basic operations for specifying retrievals and updates on db

6. Categories of Data Models • High-level or Conceptual Data models • Low-level or physical data models • Representational or implementation data models • Relational data model • Network data model • Hierarchical data model

7. Levels of Abstraction • Physical level describes how a record (e.g.: customer) is stored. • Logical level: describes data stored in database, and the relationships among the data. type customer = recordname : string;street : string;city : integer;end; • View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes.

8. Data modeling using Entity Relationship model

9. Database Schema • The logical structure of the database • Eg: the database consists of information about a set of customers and accounts and the relationship between them

10. Database Instance • The actual content of the database at a particular point in time

11. Three Schema Architecture

12. The external schema • Defines one view of data as seen by a specific set of applications or end users • The conceptual schema • Defines data from perspective of system designer • Independent of end users and data storage mechanism • The internal schema • Defines how data is organized, stored and manipulated in the application itself • Totally dependent on particular implementation

13. Data Independence • Logical Data Independence • Physical Data Independence

14. Entity • Represents a real world object or concept • Eg: an employee, a project

15. Attribute • Represents some property of interest that further describes an entity • Eg: employee’s name or salary

16. Relationship • Represents an association among 2 or more entities • Eg: an employee works on a project

17. Example of schema in the entity-relationship model

18. A Sample Relational Database

19. Data Definition Language (DDL) • Specification notation for defining the database schema • E.g. create tableaccount (account-numberchar(10),balanceinteger) • DBMS have a DDL compiler • Data dictionary contains metadata (i.e., data about data) • Database schema • Data storage and definition language • language in which the storage structure and access methods used by the database system are specified • Usually an extension of the data definition language

20. Data Manipulation Language (DML) • Language for accessing and manipulating the data organized by the appropriate data model • DML also known as query language • Two classes of languages • Procedural – user specifies what data is required and how to get those data • Nonprocedural – user specifies what data is required without specifying how to get those data • SQL is the most widely used query language

21. SQL • SQL: widely used non-procedural language • E.g. find the name of the customer with customer-id 192-83-7465selectcustomer.customer-namefromcustomerwherecustomer.customer-id = ‘192-83-7465’ • E.g. find the balances of all accounts held by the customer with customer-id 192-83-7465selectaccount.balancefromdepositor, accountwheredepositor.customer-id = ‘192-83-7465’ anddepositor.account-number = account.account-number • Application programs generally access databases through one of • Language extensions to allow embedded SQL • Application program interface (e.g. ODBC/JDBC) which allow SQL queries to be sent to a database

22. Transaction Management • A transaction is a collection of operations that performs a single logical function in a database application • Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures. • Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.

23. Example: • Consider a possible interleaving This is OK. But what about this ??????? T1: A=A+100, B=B-100 T2: A=1.06*A, B=1.06*B T1: A=A+100, B=B-100 T2: A=1.06*A, B=1.06*B

24. Storage Management • Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system. • The storage manager is responsible to the following tasks: • Interaction with the file manager • Efficient storing, retrieving and updating of data