Presentation on theme: "Learners Support Publications www.lsp4you.com A collection of conceptual tools for describing data, data relationships, data semantics, and consistency."— Presentation transcript:
Learners Support Publications A collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints. Provide a way to describe the design of a database at the logical level. Three data models that are used for database management are: 1. The Relational Data Model 2. The Hierarchical Data Model 3. The Network Data Model DATA MODELS
Learners Support Publications The Relational Data Model In this model,the data is organized into tables (ie., rows and columns). These tables are called relations. A row in a table represents a relationship among a set of values. Consider a sample database with three tables (relations):Suppliers, Items, Quantities: Suppliers (sup-no#,sup-name,status, city) Items ( item-no#, item-name, price) Quantities (sup-no#, item-no#, Qty)
Learners Support Publications Sup-no#Sup-NameStatusCity S1 S2 S3 Britannia New Cockg Delhi Mumbai Delhi Suppliers Item-no#Item-namePrice I1 I2 I3 I4 I5 I6 Milk Cake Bread Biscuit Ice cream Jam Items Sup-no#Item-no#Qty S1 S2 S3 I2 I3 I6 I4 I5 I Quantities
Learners Support Publications Rows of relations are generally referred to as tuples and the columns are usually referred to as attributes. No two tuples are identical and their ordering is not important. A relationship is represented by combining the primary key of the relations. various operations can be performed on relations such as insert new tuples, delete tuples and modify tuples. There are several languages for expressing these operations. One such language is relational query language.
Learners Support Publications The Network Data Model In this model, data is represented by collections of records and relationships among data are represented by links. Ie., the collection of records which are connected to one another by means of links. A record is a collection of fields (attributes), each of which contains only one data value. A link is an association between precisely two records. The structure of the database is shown as an arbitrary graph in which the records form the nodes and links form the edges. There is no concept of a root node.
Learners Support Publications Consider the structure of the above sample database of suppliers, items and quantities. S1Britannia10Delhi S2New30MumbaiS3Cockg10Delhi I1milk15I2cake5I3bread9I4biscuit14I5icecream6I6jam
Learners Support Publications The operations on a network database are performed through a data manipulation language for network model. The operations that can be performed on a network database include find, insert, delete, modify etc. The inserting or removing records include connect, disconnect and reconnect operations.
Learners Support Publications The Hierarchical Data Model Same as network model. The only difference is that in the hierarchical model, records are organized as trees rather than arbitrary graphs. The record type at the top of the tree is usually known as root. In general, the root may have any number of dependents and each of these dependents may have any number of low level dependents and so on. Consider the hierarchical view of the above sample database of suppliers, items and quantities.
Learners Support Publications In this tree structure supplier record type is the root node. Here the relationship is expressed in the form of a tree with all the edges pointing to the leaf. T he operations on a hierarchical database are performed through a data manipulation language for hierarchical data model. The various operations include retrieval, insertions, deletions and modifications of records.