Introduction to Relation

The relation we are going to study here is an abstraction of relations we see in our everyday life such as those between parent and child, between car and owner, among name, social security number, address and telephone number etc. We are going to focus our attention on one key property which all the everyday relations have in common, define everything that has that property as a relation, and study properties of those relations.

One of the places where relation in that sense is used is data base management systems. Along with hierarchical and network models of data, the relational model is widely used to represent data in a database. In this model the data in a database are represented as a collection of relations. Informally, each relation is like a table or a simple file. For example, consider the following table.

Name Address Home Phone
Amy Angels 35 Mediterranean Av. 224-1357
Barbara Braves 221 Atlantic Av. 301-1734
Charles Cubs 312 Baltic Av. 223-9876

Each row of this table represents a collection of data values such as name, address, and telephone number of a person. Each row is considered an instance of a relation and the table as the collection of the rows is considered a relation , which is the relation we are going to be studying in this chapter. Operations such as inserting or deleting entries to or from a table, merging two table, finding the intersection of two tables, and searching for certain entries can be described simply and precisely as operations on relations, and known mathematical results on relations can be utilized without reinventing them.
The relational model is flexible (easy to expand, easy to modify) and interface to query languages is simple. It is thus widely used today.

Next -- Binary Relation

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