Relational Model




Relational Model: -

The relational database organizes data in tables. Each table is identified by a unique table name, and is organized by rows and columns. Each column within a table also has a unique name. Columns store the values for a specific attribute, e.g. cover group, tree height.


Rows represent one record in the table. In GIS each row is usually linked to a separate feature, e.g. a forestry stand. Accordingly, each row would be comprised of several columns, each column containing a specific value for that geographic feature. In this model a key represents one or more attributes whose value can uniquely identify a record in a table. Therefore, a key common to two tables can establish connection between corresponding records in the tables.

A relational database usually contains three types 0f relationship between tables. Usually here two types of table are defined- the source table & the destination table. If the purpose is to add attribute data from a table to the feature attribute table, then the feature attribute table is the destination table and the other one is the source table. Owing ot this manner, three types of relationships can be created.

One-to-one Relationship- Here one and only one record in the destination table is related to one and only one record in the source table.

One-to-Many Relationship- This means that one record in the destination table may be related to more than one record in the source table.



Many-to-One Relationship- This type of relationship is just opposite to the One-to-Many Relationship. Here two or more records in the destination table may be related to one record in the source table.



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Last Updated on 28 September 2012