Wednesday, 8 January 2014

Terminologies used in Databases

(i) Data Item: It is the smallest unit of data. It may be derived, atomic, composite or embedded.

(ii) Database: It is a repository of stored data which is both integrated (i.e. unified with reduced redundancy) and shared.

(iii) Data Base Management System (DBMS): It records and maintains information (meaningful data). DBMS software hides all the details of data stored and present it to user in desired operation. Some functions include add, delete, read, modify, and special functions like sorting and math functions. 

(iv) DBMS software may follow hierarchical, network, or relational data model. Latest DBMS also make use of object oriented concepts and may be Object DBMS (ODBMS), Object Oriented DBMS (OODBMS) or Object Relational DBMS (ORDBMS). However, use of RDBMS is most prevalent. 

(v) RDBMS: RDBMS software is based on relational data model and follows relational algebra. RDBMS stores data about attributes of some entities in form of related tables where each table comprises of rows and columns. Some common RDBMS are MS Access, Oracle, MySQL, PostgreSQL.

(vi) Entity: Items about which relevant information is stored. For e.g. Employee, machine part etc.

(vii) Attributes & Domains: Columns of a table are referred to as attributes. A domain is a pool of values from which actual values appearing in a given column are drawn. E.g. COLOR can be an attribute in a table and values like red, orange, green etc. constitutes its domain.

(viii) Tuples & Records: Tuples in a relation represents the records which are the rows in a table. For e.g. in a table for employee, there may be records for me, you, friend etc

(ix) Schema: A schema is a logical database description and is based on types of data being used. It gives name of entities and attributes and specify the relationship between them (which could be one-one, one-many, many-many or even conditional). It is a framework into which values of data item can be fitted. Schema is DBMS independent and remains same, however, values may change over time.

(x) Keys: Some attribute or combination of attributes in a table forms the keys. These keys could be Super Key, Candidate Key, Primary Key, Alternate Key, or Foreign Key. A primary key is used to uniquely identify a record in a table. A foreign key is one which is primary key in another relation (i.e. table) and helps in linking the tables. 

(xi) Database Design: It could be conceptual, logical, or physical. A data modeler does the conceptual database design by studying and modeling the data in technology independent manner. A database designer (or may be Data Base Administrator, DBA) does the logical database design by mapping or translating the conceptual data design into logical database design to fit in the chosen data model (relational, object relational etc.). Physical database design is done by DBA by translating logical design into one or more physical design – each tailored for particular DBMS which will manage the database and particular computer system that will run the database.

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