Difference between network data model & relational data model DBs

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  sherya mathur

  Re: question in database.
  
  the difference between hierarchical data model or network data mode and relational data model:
  
  1.The hierarchical data model :The hierarchical data model organizes data in a tree structure. There is a hierarchy of parent and child data segments. This structure implies that a record can have repeating information, generally in the child data segments. Data in a series of records, which have a set of field values attached to it. It collects all the instances of a specific record together as a record type. These record types are the equivalent of tables in the relational model, and with the individual records being the equivalent of rows. To create links between these record types, the hierarchical model uses Parent Child Relationships. These are a 1:N mapping between record types. This is done by using trees, like set theory used in the relational model, "borrowed" from maths.
  
  2:the network data model :The popularity of the network data model coincided with the popularity of the hierarchical data model. Some data were more naturally modeled with more than one parent per child. So, the network model permitted the modeling of many-to-many relationships in data.
  
  3:the relational model:A database based on the relational model developed by E.F. Codd. A relational database allows the definition of data structures, storage and retrieval operations and integrity constraints. In such a database the data and relations between them are organized in tables. A table is a collection of records and each record in a table contains the same fields.
  properties of relational database: 1. Values Are Atomic 2. Each Row is Unique
  3. Column Values Are of the Same Kind
  4.The Sequence of Columns is Insignificant 5. The Sequence of Rows is Insignificant
  6. Each Column Has a Unique Name