Postgraduate Module Enterprise Database Systems Technological Educational Institution of Larisa in collaboration with Staffordshire University Larisa Dr. Theodoros Mitakos

Database properties A database represents some aspect of the real world (the miniworld or the universe of discourse) Changes to the miniworld are reflected in the database A database is a logically coherent collection of data with some inherent meaning. A random assortment of data cannot correctly be referred to as database A database is defined, built, and populated with data for a specific purpose. It has an intended group of users and some preconceived applications in which these users are interested.

Database Management System A database management system (DBMS) is a collection of programs that enables users to create and maintain a database. The DBMS is a general purpose software that facilitates the process of defining, constructing, manipulating and sharing databases among various users and applications.

Defining a database involves specifying the data types, structures and constraints for the data to be stored in the database Constructing the database is the process of storing the data itself on some storage medium that is controlled by the DBMS Manipulating the database includes such functions as querying the database o retrieve specific data, updating he database to reflect changes in the miniworld, and generating reports from the data Sharing a database allows multiple users and programs to access the database concurrently.

A DATABASE EXAMPLE STUDENTNAMESTUDENTNUMBERCLASSMAJOR SMITH171CS BROW N 82CS COURSE COURSENAMECOURSENUMBERCREDITHOURSDEPARTMENT INTRO TO COMPUTER SCIENCE CS13104CS DATA STRUCTURES CS33204CS DISCRETE MATHEMATICS MATH24103MATH DATABASE CS33803CS

DATABASE APPROACH VERSUS FILE PROCESSING Self-describing Nature of a database system Insulation between programs and data, and data abstraction Support of multiple views of the data Sharing of data and multiuser transaction processing

The database system contains not only the database itself but also a complete definition or description of the database structure and constraints. The structure of data files is stored in the DBMS catalog separately from the access programs. This property is called program-data independence. The implementation of the operations is specified separately and can change without affecting the interface (program- operation independence). Data Abstraction In traditional file processing, data definition is typically part of the application programs themselves. Any changes to the structure of the file may require changing all programs that access this file.

A database typically has many users, each of whom may require a different perspective or view of the database. A view may be a subset of the database or it may contain virtual data that is derived from the database file but is not explicitly stored. A multiuser DBMS, as its name implies, must allow multiple users to access the database at the same time. DBMS must include concurrency control software. (Online transaction processing – clerks). A transaction is an executing program or process that includes one or more database accesses such as reading or accessing database records.

Database Users Database Administrators Authorize access, coordinate and monitor the use acquire software and hardware resources. Database designers Identify the data to be stored, identify views End Users Casual users, Naive users, Sophisticated users, Stand-alone users System analysts, Application Programmers Determine requirements of end users, implement specifications as programs

Developers System designers and implementers Tool developers Operaors and maintenance personnel

Advantages of Using a DBMS Controlling Redundancy Restricting Unauthorized Access Providing Persistent Storage for Program Objects (Traditional database systems -impedance mismatch problem – data structures provided by the DBMS were incompatible with the programming language) Providing Storage Structures for Efficient Query Processing (indexes, query processing and optimization) Backup and Recovery Multiple User Interfaces (query languages, forms, menus, command codes, application interfaces, graphical user interfaces) Complex Relations among data Enforcing Integrity constraints Inferencing and Actions Using Rules (deduction rules for inferencing new information) Enforcing standards, reduced application development time, flexibility, up to date information, economies of scale

Brief History of database applications Hierarchical and Network systems (intermixing of conceptual relations with the physical storage) Relational Databases Object Oriented Applications Interchanging Data on the Web

New Applications Scientific Images Videos Data mining Spatial Time series Complex data structures New data types New operations and query languages New storage and indexing structures

When not to use a DBMS High initial investment in hardware, software, training, security The applications are simple and not expected to change Strict real time requirements Multiple-user access to data is not required.

Terminology Data model (a collection of concepts that can be used to describe the structure of the database-data types, relations, constraints + operations, behavior) High or conceptual level, low or physical data models (record formats, access paths), representational models (relational, network, hierarchical) Entity ( a real world concept) Attribute a property of interest Relationship among two or more entities is an association among the entities.

Database schema (intension) is called the description of the database Database state or snapshot (the data in the database a particular moment) Valid state (extention) (a state that satisfies the structure and constraints specified in the schema) Three-schema architecture  Internal level (describes the physical storage structure of the database-uses a physical data model)  Conceptual level (describes the structure of the whole database for a community of users, concentrates on describing entities, data types, relationships)  External or View level (includes a number of external schemas that describes the part of the database that a particular user group is interested)

Data independence Logical data independence (is the capacity to change the conceptual schema without having to change external schemas or application programs e.g. expand the database by adding a new data type) Physical data independence (is the capacity to change the internal schema without having to change the conceptual schema e.g. some files have to be reorganized)

Database Languages and Interfaces Data definition Language (DDL) is the language used to define conceptual and internal schemas. Storage definition language is the language used to define internal schemas. View definition language is used to specify user views and their mappings Data manipulation language (DML) is used to for data retrievals, insertions, deletions  High level or non procedural DML (used on its own) query language  Low level or procedural DML (embedded in a general purpose programming language – host language)

Menu-based interfaces for web clients or browsing Form-based interfaces Graphical user interfaces Natural language interfaces Interfaces for parametric users Interfaces for the DBA

Architectures for DBMS Centralized DBMS Architecture Basic Client/Server Architecture Two-tier client server Architecture Three-tier Client/server Architecture

Classification of DBMS According to the data model (relational, object oriented, network, hierarchical) According to number of users (Single user, Multiuser) According to the number of sites over which database is distributed (centralized, distributed) (homogeneous, heterogeneous) Cost Purpose