Describing & Storing Data from Dbms

Topics: Database, Relational model, Database model Pages: 5 (1240 words) Published: March 7, 2011



Topic: Describing & Storing Data In DBMS

(Traditional Models)


A computer database relies upon software to organize the storage of data. This software is known as a database management system (DBMS). Database management systems are categorized according to the database model that they support. The model tends to determine the query languages that are available to access the database. A great deal of the internal engineering of a DBMS, however, is independent of the data model, and is concerned with managing factors such as performance, concurrency, integrity, and recovery from hardware failures. In these areas there are large differences between products. A Relational Database Management System (RDBMS) implements the features of the relational model outlined above. In this context, Date's "Information Principle" states: "the entire information content of the database is represented in one and only one way. Namely as explicit values in column positions (attributes) and rows in relations (tuples). Therefore, there are no explicit pointers between related tables."

Definition of Describing & Storing Data in DBMS

The user of a DBMS is ultimately concerned with some real-world enterprise, and the data to be stored describes various aspects of this enterprise. For example, there are students, faculty, and courses in a university, and the data in the university database describes these entities and their relationships.

There are three types of describing & storing data in DBMS:

Data Models

Level of Abstraction

Data Independency

Data Models

A database model or database schema is the structure or format of a database, described in a formal language supported by the database management system. Schemas are generally stored in a data dictionary. Although a schema is defined in text database language, the term is often used to refer to a graphical depiction of the database structure. There are three types of data models:

File Based Models

Traditional Models

Semantic Models

Traditional Models

There are three types of traditional models:

Hierarchichal Model

Network Model

Relational Model

Hierarchical model

Hierarchical Model.
In a hierarchical model, data is organized into a tree-like structure, implying a single upward link in each record to describe the nesting, and a sort field to keep the records in a particular order in each same-level list. Hierarchical structures were widely used in the early mainframe database management systems, such as the Information Management System (IMS) by IBM, and now describe the structure of XML documents. This structure allows one 1:N relationship between two types of data. This structure is very efficient to describe many relationships in the real world; recipes, table of contents, ordering of paragraphs/verses, any nested and sorted information. However, the hierarchical structure is inefficient for certain database operations when a full path (as opposed to upward link and sort field) is not also included for each record. One limitation of the hierarchical model is its inability to efficiently represent redundancy in data. Entity-Attribute-Value database models like Caboodle by Swink are based on this structure. Parent–child relationship: Child may only have one parent but a parent can have multiple children. Parents and children are tied together by links called "pointers“. A parent will have a list of pointers to each of their children.

Network model

Network Model.

The network model organizes data using two fundamental constructs, called records and sets. Records contain fields (which may be organized hierarchically, as in the programming language COBOL). Sets (not to be confused with mathematical sets) define...
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