A Survey of Automatible Schema Mapping

Not all schema mapping is necessarily difficult to perform with computers. Some types of schemas are nicely translatable to other types of schemas, which opens the door for using software to produce the mappings.

What makes this feasible is that in these cases, mapping patterns have been identified that preserve data model semantics without requiring the map-writing software to care about the details of the data model semantics.

Examples appear below.

• Mapping hierarchical schemas to relational schemas
  Consider a hierarchical type schema like HTML, and a relational type schema like SQL.

  Generally, HTML has is a tree of nodes. Each node has a set of attributes name/value pairs and a set of children nodes.

  On naive mapping is possible: Create a SQL table where one row corresponds to each node from the HTML schema. The tree structure is preserved by having a column in the table that lists the primary key of the row that corresponds to each child node.

• Mapping relational schemas to object-oriented schemas
  One solution is to define one object class per relation. Create one instance of each class to model each row that appear in the corresponding relation.

  Relational view definitions and calculated values can be expressed with methods in the object-oriented system.