Introduction to Databases

Case Example: File based Processing Real Estate Agent’s office Property for sale or rent Potential Buyer/renter Staff/employees

Queries 3-bed room apts for sales? Flats within 3 miles of the city? Average price of house? Average rent for 2 BR flat? Total annual salary for staff?

Reports Expected monthly turnover of renters? This month’s turnover compare to the last month?

Files in Sales Dept Selling and renting of properties Property_for_rent (Pno, Street, Area, City, Pcode, Type, Rooms, Rent, Ono) Owner (Ono, Fname, Lname, Address, Tel_no, Pref_Type, Max_rent) Potential renters Renter (Rno, Fname, Lname, Address, Tel_No, Pref_Type, Max_rent)

Files in Contract Dept Lease(Lno, Pno, Rent, Payment, Deposit, paid, Start, Finish, Duration) Property_for_rent (Pno, Street, Area, City, Pcode, Rent) Renter (Rno, Fname, Lname, Address, Tel_No) Data entry File maintenance Reports generation

Another example Payroll Dept Staff_salary(Staff No, First Name, Last Name, Address, Date_of_Birth, Salary, National Insurance Number, Branch Number) Personnel Dept: Staff(Staff No, First Name, Last Name, Address, Telephone Number, Position, Date_of_Birth, Salary, National Insurance Number, Branch Number)

File Based Processing Sales Contracts Data entry and reports File handling routines File definition Sales application programs Contracts application programs

Limitations of File-Based Processing Separation and Isolation of data Duplication of data Data dependence Incompatibility of files Fixed queries/ proliferation of application programs

Database “A shared collection of logically related data (and a description of this data) designed to meet the information needs of an organization.”

Entity Relationship Diagram Staff Property_for _Rent Branch Owner Viewing Renter Takes Requests Has Owns Oversees IsAllocated

Parts of ER diagram Six entities (the rectangles): Branch, Staff, Property_for_Rent, Owner, Renter and Viewing. Six relationships (the diamonds): IsAllocated, Has, Overseas, Owns, Requests, and Takes

DBMS “ A software system that enables users to define, create and maintain the database and provides controlled access to this database.” Data definition Language (DDL): data types, structures and constraints on the data. Data Manipulation Language (DML): insert, update, delete, and retrieve data Query Language: general enquiry facility

Two types of DML: –Procedural: manipulates the database record by record. –Non-Procedural: operates on a set of records. Most common is Structured Query Language (SQL) Controlled Access to the database: –security system –integrity system –Concurrency controlled, shared access –recovery control system –user accessible catalog

Database Processing Sales Contracts Data entry and reports DBMS Database Sales application programs Contracts application programs Property, Owner, Renter and Lease details + File Definitions

Components of DBMS environment HardwareSoftwareProceduresPeople Data BridgeMachineHuman

Hardware Some DBMS run only on particular hardware and operating systems Minimum amount of main memory and disk space to run Client -Server architecture: –Central computer runs the backend of the DBMS –Other computers run the frontend

Dream Home hardware configuration Database serverEastern Office Western Office Southern Office Northern Office Database

Software The DBMS software Application programs: C, COBOL, Fortran, Ada etc. Using a fourth level language such as SQL Fourth generation tools: –rapid development of applications –non-procedural query languages –report generators –form generators –graphic generators –application generators Fourth generation tools can improve productivity.

Data The structure of the database is called the schema. Tables: Property_for_Rent, Owner, Renter and Lease Attributes System Catalog contains: –Names, types, and sizes of data items –Integrity constraints on data –Names of authorized users who have access to the data –What indexes and storage structures are being used- Tree structures.

Procedures: Log on to the DBMS Use particular DBMS facility or application program Start and stop the DBMS Make backup copies of the database Handle hardware and software failures Change the structure of the table, reorganize the data across multiple disks, improve performance, or archive data to secondary storage. PEOPLE: DB engineers, DB designers, DB developers/ programmers

Data and database administrators Data Administrator (DA) –management of data (database planning, development, maintenance of standards, policies, procedures and conceptual and logical database design). Database Administrators: –Physical database design and implementation, security and integrity control, maintanence of the operational system and ensuring satisfactory performance for the applications and users.

Database designers Logical database designers: –Entities, attributes, relationships, constraints Business rules Physical database designers: –Decides how it is to be physically realized.

Application Programmers Retrieving, inserting, updating and deleting Programs –Third Generation Language (3GL) –Fourth Generation Language (4GL) End Users: –Inexperienced Users –Sophisticated users

The Paradigm Shift The structure of the database is determined using the database design. Paradigm shift: think of the data first and the application later. Poorly designed database --> errors Well designed database --> correct information A complete methodology for database design. –Entity- Relationship diagram –Guidelines to help identify the entities, attributes and relationships

Advantages of Databases Control of data redundancy Data consistency More information from the same amount of data Sharing the data Improve data integrity and improve security Enforce standards Economies of scale Balance the conflicting requirements Improve data accessibility and responsiveness Increase productivity Improve maintenance through data interdependencies (pgm-data independence) Increase concurrency Improve backend recovery services

Disadvantages of Databases Complexity Size Cost of DBMS Additional hardware costs Cost of conversion Performance High impact of a failure