1 A data schema, especially a data subschema in a relational data system.

2 A subschema is a description of only that portion of the database pertinent to a particular user's needs.

3 Digraph will be constructed by using the dependence of the left of subset's FD. Some nodes will help to decompose a subschema of BCNF. The key of the subschema is the left or left's equivalence.

4 We must distinguish between a record type and a instance of the data-item types and record types stored in a database the term subschema refers to an collocation programmer's vies of the data he uses.

5 This artical is mainly expatiate on the process how foregrounding subschema been designed and run.