database models

DATA MODELS

Data model is a collection of logical constructs used to represented to data structure and data relationships found with in the databases . Database models can be grouped into two (2) categories. These are

1. Record based logical model  (or) implementation model.
2. Object based  logical model (or) conceptual model.
3. E-R (Entity – Relationship ) model.

Record based logical model / Implementation model: This model emphases on how the data are represented in the database. It has 3 (three) types. These are

1. Hierarchical data model.
2. Network data model.
3. Relational data model.

Hierarchical data model  we can represent the data as a tree model . The origin of data tree is the root . The data is located at different level along a particular branch from the root is called  is node . the last node in the series is called leaf . It supports one-to-many relationship.

 

 The main idea behind Network data model   is to bring about many-to many relationship . This relationship between the different data items . These are called as sets. In this we use a pointer to locate a particular record

The above diagram  describes the vendor and item relationship should be represents in Network model in this it describes  which vendor is selling a particular item.

Dr.E.F.CODD first introduced the relational database data model in 1970. this model allows  the data to be represented in a simple row and column format, table. A system which consist database in the form of tables is RDBMS.

      Each table indicating an entity , table consists rows and columns . Each column 

      indicates record or data of entity and each column indicates attribute or field.

Eg:

Vendor No	Vendor Name	Item
111	Ram	Mouse
121	Shyam	Keyboard
131	Arun	Monitor

Conceptual Data model or Objective based logical model: This model is consider with the represented in the database rather than how data is represented in an organization .It also included Entity Relationship model and uses this model in three types of relationships . These are

One-to-one Relationship: This type of relationship mainly has to represent the relationship between two set values and these set values have a relationship between one set to another set values  and specify the one-to-one relationship is shown as in the below. .Eg:

                  Set A               Set B

                  1          à        a

                  3          à        b

                  9          à        d         

One-to-many Relationship:  This type of relationship mainly has to represent the relationship between two set values and  the single value of one set should be participate in the relationship with another set of  two different values and form One-to-many relationship . In this way   the second set of more than one values should be  traced with single value of first set . Eg:

 

Many-to-Many Relationship: These types of relationship mainly have to represent the relationship between two set values and the value of the first set  should be participate in the relationship with more than single values of another set values and the same time  the value of second set should be traced with more than one value and form a Many-to-Many Relationship. Eg:

 

E-R Model (Entity-Relationship Model): Entity Relationship model consist of entities and specify the relationship among one or more than one entities and form a Entity Relationship Model. Overall logical structure of a DBMS can be expressed graphically by on E-R diagram which consist the following components. Eg:

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