Database lecture 01 introduction, Slides of Database Management Systems (DBMS)

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Database Systems

Khwaja Fareed University of Engineering &

IT

Lecture 1 Lecture 1

Fundamental Database Concepts Fundamental Database Concepts

A database is any collection of data.  A DBMS is a software system designed to maintain a database.  We use a DBMS when  (^) there is a large amount of data  (^) security and integrity of the data are important  (^) many users access the data concurrently

With all that data, AT&T must be concerned with questions such as:  (^) Where is the information kept?  (^) How is the data structured?  (^) How is the data kept consistent?  (^) How is the data described?  (^) How is the data kept secure?  (^) How do different pieces of data interrelate?

Without a DBMS, we'd have: data stored as bits on disks organized as files Access by a collection of ad hoc programs in C++, Java, PHP, etc. users of the data There is no control or coordination of what these programs do with the data

data users of the data data dictionary data definition processor query processor security manager concurrency manager index manager application program(s) application program(s) application program(s) application program(s) internal/implementation view external/application view DBMS software components data description

users of the data application program(s) application program(s) application program(s) application program(s) data data dictionary data definition processor query processor security manager concurrency manager index manager DDL: data definition language system configuration languages QL: query language DML: data manipulation language GPL: general purpose languages

users of the data application program(s) application program(s) application program(s) application program(s) data data dictionary data definition processor query processor security manager concurrency manager index manager software operating between the data and the applications can provide many capabilities in a generic way

A DBMS supports access by concurrent users  (^) concurrent = happening at the same time  (^) concurrent access, particularly writes (data changes), can result in inconsistent states (even when the individual operations are correct)  (^) the DBMS can check the actual operations of concurrent users, to prevent activity that will lead to inconsistent states

A DBMS can restrict access to authorized users  (^) security policies often require control that is more fine-grained than that provided by a file system  (^) since the DBMS understands the data structure, it can enforce fairly sophisticated and detailed security policies  (^) on subsets of the data  (^) on subsets of the available operations

A DBMS supports representation of complex relationships and integrity constraints  (^) the semantics (meaning) of an application often includes many relationships and rules about the relative values of subsets of the data  (^) these further restrict the possible instances of the database  (^) relationships and constraints can be defined as part of the schema

A DBMS can provide backup and recovery  (^) backup = snapshots of the data particular times  (^) recovery = restoring the data to a consistent state after a system crash  (^) the higher level semantics (relationships and constraints) can make it difficult to restore a consistent state  (^) transaction analysis can allow a DBMS to reconstruct a consistent state from a number of backups

persistent objects, types and data structures  control of concurrent users  controlling of redundancy  restricting access (security)  representation of complex relationships and integrity constraints  backup and recovery  multiple user interfaces and user views