Data: Facts, figures, statistics etc. having no particular meaning (e.g. 1, ABC, 19 etc).
Record: Collection of related data items, e.g. in the above example the three data items had no meaning
What is a Database?
A collection of related pieces of data:
Representing/capturing the information about a real-world enterprise or part of an enterprise.
Collected and maintained to serve specific data management needs of the enterprise
Activities of the enterprise are supported by the database and continually update the database
University Database: Data about students, faculty, courses, research-laboratories, course registration/enrollment etc.
Reflects the state of affairs of the academic aspects ofthe university.
Purpose: To keep an accurate track of the academic activities of the university.
DATABASE MANAGEMENT SYSTEM (DBMS):
A general purpose software system enabling:
Creation of large disk-resident databases.
Posing of data retrieval queries in a standard manner.
Retrieval of query results efficiently.
Concurrent use of the system by a large number of users in a consistent manner.
Guaranteed availability of data irrespective of system failures.
OS FILE SYSTEM STORAGE BASED APPROACH
•Files of records -used for data storage
•data redundancy -wastage of space
•maintaining consistency becomes difficult
•Record structures -hard coded into the programs
•structure modifications -hard to perform
•Each different data access request (a query)
•performed by a separate program
•difficult to anticipate all such requests
•Creating the system
•requires a lot of effort
•Managing concurrent access and failure recovery are difficult
•separation of data and metadata
•flexibility of changing metadata
Data access language
•ad-hoc query formulation -easy
•less effort required
•concentration on logical level design is enough
•components to organize data storageprocess queries, manage concurrent access, recovery from failures, manage access control are all available
Collection of conceptual tools to describe the database at a certain level of abstraction.
Conceptual Data Model
high level description
useful for requirements understanding.
Representational Data Model
describing the logical representation of datawithout giving details of physical representation.\
Physical Data Model
description giving details about record formats,file structures etc.
A relation is a data structure which consists of a heading and an unordered set of tuples which share the same type.
A relation has zero or more tuples.
A relation value is an instance of a relation.
A relation variable (relvar) is a variable which has a relation value.
In SQL, a database language for relational...