Introduction To DBMS

Information is data that have been put into a meaningful and useful context and communicated to recipient who uses it to make decisions. Information helps in eliminating irrelevant and poor data. More useful and intelligent form. Integration of information is needed in MIS is done through DBMS

Difference between Data and information Input(Data) Process Information (Output)

Key attributes of Information Accuracy- free from mistakes and errors, clear Timeliness- within given time frame Relevancy- use of information for particular person

Information processing Information Processing is the acquisition storage, organization, retrieval, display and dissemination of information People Goals Information Physical Resources

Finance R&D Production Production Planning Marketing Sales and distribution production

Data – raw facts Information- refined data Field – a character or group of characters (alphanumeric or numeric) that has a specific meaning Record – a set of one or more logically related fields File – a set of related records

Stages of Information System Stage 0: Manual Information System Records Files Index Cards Stage 1: Sequential Information Systems Tapes slow, non-interactive, redundancy,... . Stage 2: File Based Information Systems Disk (direct access) application program has its own file data dependence data redundancy Stage 3: DBMS based Information Systems Generalized data management software Transaction processing

File Systems Input Application program Data file Output

File based systems Problems: Data is stored in files Each file has a specific format Programs that use these files depend on knowledge about that format Problems: No standards Data duplication Data dependence No way to generate ad hoc queries No provision for security, recovery, concurrency, etc.

Disadvantages of File Approach Data and application dependence Data isolation Data redundancy Redundant storage Anomalies Data inconsistency Violation of data integrity

Drawbacks of using file systems Data redundancy and inconsistency Multiple file formats, duplication of information in different files Difficulty in accessing data Need to write a new program to carry out each new task Data isolation — multiple files and formats Integrity problems Integrity constraints (e.g. account balance > 0) become part of program code Hard to add new constraints or change existing ones

Drawbacks of using file systems (cont.) Atomicity of updates Failures may leave database in an inconsistent state with partial updates carried out E.g. transfer of funds from one account to another should either complete or not happen at all Concurrent access by multiple users Concurrent accessed needed for performance Uncontrolled concurrent accesses can lead to inconsistencies – E.g. two people reading a balance and updating it at the same time Security problems Database systems offer solutions to all the above problems

Collection of interrelated data Set of programs to access the data DBMS contains information about a particular enterprise DBMS provides an environment that is both convenient and efficient to use. Database Applications: Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Databases touch all aspects of our lives

Database Definition Database : is a collection of data, typically describing the activities of one or more related organizations is a collection of logically related files a collection of data and information describing items of interest to an organization A database is a collection of information DBMS: is a software designed to assist in maintaining and utilizing large collection of data A database management system (DBMS) is the software than controls that information

Purpose of Database Systems Database management systems were developed to handle the following difficulties of typical file-processing systems supported by conventional operating systems: Data redundancy and inconsistency Difficulty in accessing data Data isolation – multiple files and formats Integrity problems Atomicity of updates Concurrent access by multiple users Security problems

DBMS Functions Data management: Maintaining data independence storage management integrity management manipulation Maintaining data independence Security management Concurrency control Recovery management Database communication support M.G. Erechtchoukova

Data Redundancy Data inconsistency exists when different and conflicting versions of the same data appear in different places.

Data Independence External Schema 2 External Schema 3 Logical data independence Conceptual Schema Physical data Physical Schema independence Secondary Storage

Data Independence (cont…) Logical data independence – the immunity of the external schemas to changes in the conceptual schema Physical data independence – the immunity of the conceptual schema to changes in the physical schema M.G. Erechtchoukova

Data Dictionary Meta-data: Data about users and authorization Descriptions of data items and relationships among them Integrity constraints Data about users and authorization Used by DBMS to implement data processing The dictionary or catalog stores information about the database itself This is data about data or ‘metadata’ Almost every DBMS uses the dictionary

Data Integrity Correctness and accuracy of the data E.g.Primary key constraint

Schema Schema – the logical structure of the database e.g., the 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

Instances 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.