Data Models and Data Model Concepts

Data Model

• A set of concepts to describe the structure of a database and certain constraints that the database should obey.
• A description of the way that data is stored in a database.
• Helps to understand the relationship between entities and to create the most effective structure to hold data.
• A collection of tools or concepts for describing data, data relationships, data semantics, and data constraints.

Categories of Data Models

• Object-based
• Record-based
• Physical-based

Record-based Data Models

• Consist of a number of fixed format records.
• Each record type defines a fixed number of fields; each field is typically of a fixed length.

Hierarchical Data Model

• The simplest data model.
• Record type is referred to as node or segment.
• Nodes are arranged in a hierarchical structure as a sort of upside-down tree.
• A parent node can have more than one child node.
• A child node can only have one parent node.
• The relationship between parent and child is one-to-many.
• Relation is established by creating physical link between stored records.

Advantages of Hierarchical Data Model

• Simple to construct and operate on.
• Corresponds to a number of natural hierarchically organized domains.

Disadvantages of Hierarchical Data Model

• Navigational and procedural nature of processing.
• Database is visualized as a linear arrangement of records.
• Little scope for "query optimization".

Network Data Model

• Allows record types to have more than one parent unlike hierarchical model.
• A network data model sees records as set members.
• Each set has an owner and one or more members.
• Allow many to many relationship between entities.

Advantages of Network Data Model

• Able to model complex relationships and represents semantics of add/delete on the relationships.
• Can handle most situations for modeling using record types and relationship types.
• Language is navigational; uses constructs like FIND, FIND member, FIND owner, FIND NEXT within set, GET etc.

Disadvantages of Network Data Model

• Navigational and procedural nature of processing.
• Database contains a complex array of pointers that thread through a set of records.
• Little scope for automated "query optimization”.

Relational Data Model

• Developed by Dr.Edgar Frank Codd in 1970.
• Terminologies originate from the branch of mathematics called set theory and relation.
• Can define more flexible and complex relationship.
• Viewed as a collection of tables called “Relations” equivalent to collection of record types.
• Relation: Two dimensional table that stores information or data in the form of tables.
• A row of the table is called tuple (equivalent to record).
• A column of a table is called attribute (equivalent to field).