Introduction to Data Base

Keeping Records

- Mankind has been keeping records since the dawn of civilization (purely pictorial)
- then into the alphabetic systems
- quantitative (numerical and financial) information was kept in lists.
- later these lists took on a more structured form (rows and columns) called ledger
- these records were maintained by hand, usually on paper, dozens of clerks
- computer has changed all this
- almost every organization now keeps its records in electronic form and process them using a computer system
- army of clerks is no longer required
- introduction of the computer has led to major changes in employment pattern
- employment pattern shift away from primary industries (agriculture and manufacturing) to service
- this trend has been accelerated by the increasing use of IT (computers and electronic communications)
- at the heart of these computerized information processing systems you will find a DATABASE

Data and Information


What is Data?
- individual facts about something or somebody that have not been organized (raw data)
- a random collection of names and telephone numbers is just data
What is Information?
- data that has been organized in such a way as to be useful to somebody
- the telephone directory contains information because it has been organized
- information to one person in a particular circumstance may be simply considered as data to another

Information processing
Key aspects key aspects
- capturing data (forms for capturing data (forms for data capture )
- storing data (tables for data storage) storing data (tables for data storage)
- processing data (queries, macro and programs) processing data (queries, macro and programs)
- communicating information (Reports for communicating communicating information (Reports for communicating information)
What is Database?
- combination of software and data that are used to perform combination of software and data that are used to perform
above four key aspect of information processing above four key aspect of information processing
- computers are not the only means of storing data and computers are not the only means of storing data and producing information producing information
- An integrated collection of data organized to meet the An integrated collection of data organized to meet the needs of one or more users needs of one or more users

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.
Eg. type customer = record
name : string;
street : string;
age : integer;
end;
- View level: application programs hide details of data types. Views can also hide information (e.g. account balance) for security purposes.

Instances and Schemas
- Similar to types and variables in programming languages
- Schema – the logical structure of the database (a complete example will be given in SQL lecture)
• e.g., the part of the bank database consists of information about a set of customers and accounts and the relationship between them)
• Analogous to type information of a variable in a program
• Physical schema: database design at the physical level
• Logical schema: database design at the logical level
- Instance – the actual content of the database at a particular point in time
• Analogous to the value of a variable
- Physical Data Independence – the ability to modify the physical schema without changing the logical schema
• Applications depend on the logical schema
• In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.

Data Models
- A collection of tools for describing
• data
• data relationships
• data semantics
• data constraints
- Entity-Relationship model (we will discuss in this module)
- Relational model (we will discuss in this module)
- Other models:
• object-oriented model
• semi-structured data models
• Older models: network model and hierarchical model

Entity Relationship model
- E-R model of real world
Entities (objects)
• E.g. street block,street,parcel
Relationships between entities
• Relationship set depositor associates customers with accounts
- Widely used for database design
• Database design in E-R model usually converted to design in the
relational model which is used for storage and processing