1. Most databases set up multiple tables to avoid duplication of information in the database, because only the information of a specific topic is stored in one table once. Two tables can be related when information that is not contained in the current table is required.
2. ArcGIS allows records in one table to be associated with records in another table through a common field. Such associations can be made in a number of ways, including temporarily joining or associating tables in a map, or creating relationship classes in a geodatabase that can maintain longer-term associations. For example, a table of parcel ownership information can be associated with a parcel map layer because they share a parcel ID field.
3. Joining: When joining two tables, attributes can be appended from one table to another based on the common fields of the two tables, thereby forming a feature class (data table) with complete information.
4. Association: Association tables are also used to define a relationship between two tables - which is also based on common fields - but do not append attributes from one table to another, but instead access the associated data when needed.
5. When there is a one-to-one or many-to-one relationship between the data in the two tables, the two tables can be connected. When there is a one-to-many or many-to-many relationship between the data in the two tables, the two tables can be related.