INTRODUCTION TO DATABASE MANAGEMENT SYSTEMS By Mohammed Sanaulla Khan SID: 1120297 Mohammed Mudassaruddin SID: 1111422 Abstract A collection of programs that enables you to store, modify, and extract information from a database. There are many different types of DBMSs, ranging from small systems that run on personal computers to huge systems that run on mainframes. The following are examples of database applications: ? computerized library systems ? automated teller machines ? flight reservation systems ? computerized parts inventory systems
From a technical standpoint, DBMSs can differ widely. The terms relational, network, flat, and hierarchical all refer to the way a DBMS organizes information internally. The internal organization can affect how quickly and flexibly you can extract information. Introduction A database consists of four elements as given, 1. Data 2. Relationships 3. Constraints 4. Schema 1) Data ? Data are binary computer representations of stored logical entities. ? Software is divided into two general categories-data and programs. ? A program is a collection of instruction for manipulating data. Data exist is various forms- as numbers tents on pieces of paper, as bits and bytes stored in electronic memory or as facts stored in a persons mind. 2) Relationships ? Relationships explain the correspondence between various data elements. 3) Constraints ? Are predicates that define correct database states. 4) Scheme ? Schema describes the organization of data and relationships within the database. ? Schema defines various views of the database for the use of various system components of the database management system and for the application’s security. A schema separates physical aspects of data storage form the logical aspects of data representation. [pic] Types of schema ? Internal schema: defines how and where the data are organized in physical data storage. ? Conceptual schema: defines the stored data structures in terms of the database model used. ? External schema: defines a view (or) views of the database for particular uses. ? In database management systems data files are the files that store the database information whereas offer files, such as index files and data dictionaries, store administrative information known as metadata.
Data base are organized by fields, records and files. i) Fields: is a single piece of information. ii) Record: is one complete set of fields. iii) File: is a collection of records. Advantage of Data in database Database system provides the organization with centralized control of its data Redundancy can be reduced: In non-database systems, each application (or) department has its own private file resulting in considerable amount of redundancy (or) the stored data. Thus storage space is wasted. By having centralized database most of this an be avoided Inconsistency can be avoided: When the same data is duplicated and changes are made at one site, which is not propagated to the other sites, it gives rise to inconsistency. If the redundancy is removed chances of having inconsistent data is removed. Data can be saved: The existing application can save the data in a database. Standards can be enforced: With the central control of the database, the database administrator can Enforce standards. Integrity can be maintained Integrity means that the data in the database is accurate.
Centralized control of the date helps in permitting to define integrity constraints to the data in the database. Characteristics of Data in a Database The data in a database should have the following features: 1. Shared – Data in a database are shamed among different users and applications. 2. Persistence – Data in a database exist permanently in the sense the data can live beyond the scope of the process that created it. 3. Validity / Integrity / Correctness – Data should be correct with Respect to the real worlds entity that they represent. . Security – Data should be protected from unauthorized access. 5. Consistency- whenever more than are database represents related real – world valves, the valves should be consistent with respect to the relationship. 6. Non –redundancy – No two data items in a database should represent the same real world entity. 7. Independence – The three levels in the schema (internal, conceptual and external) should be independent of each other so that the changes in the schema at one level should not affect the other levels. Database Management System
A database management system (DBMS) is a collection of programs that enables you to store modify and extract information form a database. The following are the examples of database application 1. Computerized library systems 2. Automated teller machines 3. Flight reservation systems 4. Computerized parts inventory systems. Components of a DBMS Database I) Transaction Management A transaction is a sequence of database operations that represents a logical unit of work and that accesses a database and transforms it from one state to another.
A transition can update a record, delete (or) modify a set of records etc. ii) Concurrency control Concurrency control is the database management activity of co-ordinating the actions of database manipulating process that separate concurrently that access shared data and can potentially interfere with one another. iii) Recovery Management The recovery management system in a database ensures that the aborted or failed transactions create non adverse effect on the database or the other transitions. iv) Security Management Security refers to the protection of data against unauthorized access.
Security mechanism of a DBMS make sure that only authorized users are given access to the data in the database v) Language Interface The DBMS provides support languages used for the definition and manipulation of data in the database. The data structures are created using the data definition language commands. The data manipulation is done using the data manipulation commands. vi) Storage Management The DBMS provides a mechanism for management of permanent storage of the data. The internal schema defines how the data should be stored by the storage management mechanism and this storage manager interface with the perating system to access the physical storage. vii) Data Catalog Management Data catalog or Data Dictionary is a system database that contains descriptions of the data in the database (metadata). If contains information about data, relationships, constraints and the entire schema that organize these features in to a unified database. Transaction Management ? A transaction is a collection of operations that performs a single logical function in a database application. ? Each transaction is a unit of both atomicity and consistency.
Thus, we require that transactions do not violate any database consistency constraints. ? That is, if the database was consistent when a transaction started, the database must be consistent when the transaction successfully terminates. ? However, during the execution of a transaction, it may be necessary temporarily to allow inconsistency. This temporary inconsistency, although necessary, may lead to difficulty if a failure occurs. ? It is the responsibility of the programmer to define properly the various transactions, such that each preserves the consistency of the database. For example, the transaction to transfer funds from account A to account B could be defined to be composed of two separate programmes; one that debits account A, and another that credits account B. ? The execution of these two programs one after the other will indeed preserve consistency. ? However, each program by itself does not transform the database from a consistent state to a new consistent state. ? Thus, those programs are not transactions. Storage Management ? Databases typically require a large amount of storage space. Corporate data bases are usually measured in terms of gigabytes or, for the largest databases, terabytes of data. ? A gigabyte is 1000 megabytes (1 billion bytes), and a terabyte is 1 million megabytes (1 trillion bytes). ? Since the main memory of computers cannot store this much information, the information is stored on disks. Data are moved between disk storage and main memory as needed. ? Since the movement of data to and from disk is slow relative to the speed of the central processing unit, it is imperative that the database system structure the data so as to minimize the need to move data between disk and main memory. The goal of a database system is to simplify and facilitate access to data. ? High – level views help to achieve this goal. ? A storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system. ? The storage manager is responsible for the interaction with the file manager. ? The raw data are stored on the disk using the file system, which is usually provided by a conventional operation system. ? The storage manager translates the various DML statements into low-level file-system commands. Thus, the storage manager is responsible for storing, retrieving, and updating of data in the database. Data Modeling ? The two main purposes of data modeling are, i) To assist in the understanding of the meaning (or) semantic of the data. ii) To facilitate communication about the information requirements. ? A data model makes it easier to understand the meaning of the data and thus we model data to ensure that we understand: i) Each users perspective of the data ii) The nature of the data itself, independent of its physical representations. iii) The use of data across application areas.
An optimal data model should satisfy the criteria listed below: i) Structural validity – consistency with the way the organization defines and organizes information. ii) Simplicity – Ease of understanding by information system Professionals and non-technical users. iii) Expansibility – Ability to distinguish between different data, relationships between data and constraints. iv) Non-redundancy-Exclusion of extraneous information, v) Sharability-Not specific to any particular application or technology and thereby usable by many. vi) Extensibility – Ability to evolve to upport new requirements with minimal effect on existing users. vii) Integrity – consistency with the way the organization uses and manages information. ? Four database model: i) Hierarchical Model ii) Network model iii) Relational model iv) Object – oriented. v) Object relational model vi) Deductive / Inference Model 2. Network Model: ? The Network model replaces the hierarchical tree with a graph this allowing more general connections among the modes. ? The main difference of the network model from the hierarchical model is its ability to handle many-to many (n:n) relationship. In n/w database terminology, a relationship is a set, Each set is made of atleast two types of records: an owner record (parent) and a member record (child). 3. Relation model: ? Relational model stores the data is the form of a table. ? A single database can be spread across several tables. ? A relational model uses tables to organize data elements. ? Each table corresponds to an application entity and each row represents an instance of that entity. 4. Object oriented Model: ? Object – oriented Model represents an entity as a class. A class represents both object attributes as well as behaviour of the entity 5. Entity-Relationship Model ? A database can be modeled as: o a collection of entities, o relationship among entities. ? An entity is an object that exists and is distinguishable from other objects. o Example: specific person, company, event, plant ? Entities have attributes o Example: people have names and addresses ? An entity set is a set of entities of the same type that share the same properties. o Example: set of all persons, companies, trees, holidays [pic] Rectangles represent entity sets. ? Diamonds represent relationship sets. ? Lines link attributes to entity sets and entity sets to relationship sets. ? Ellipses represent attributes o Double ellipses represent multivalued attributes. o Dashed ellipses denote derived attributes. ? Underline indicates primary key attributes ———————– Data items Relationships Data base Constraints Schema Data Catalog Management Application Transaction Management Concurrency Control Recovery Management Security Management Language Interface Data Access Storage Management