What is a Schema?
Schemas can be defined on different levels of abstraction:
- Logical schema - describes the concrete data
format (syntax)
- e.g. XML schema, database schema
- Conceptual schema - describes the concepts
- e.g. UML, Ontologies
- defines classes/types and their properties and relations
- can be abstracted from a logical schema in most cases
In hale»studio we define the schema mapping on the conceptual level,
between classes/types and properties. For the complete transformation
process however, information about the data format is needed. The
approach used in hale»studio can deal with both kinds of schemas,
abstracting a conceptual view for logical schemas, while using the
information from the logical schema for the transformation process.
For conceptual schemas, no transformation can be applied, but the
mapping can be exported or reused for logical schemas that were
derived from the conceptual schema.
Logical schemas are usually more readily available compared to
conceptual schemas, as they describe how the actual data is stored,
and are either defined explicitly or can even be derived from the
existing data structure.
A schema defines a set of types or classes. Each type has a
set of properties. A property either has an associated property type
or is a group of properties. Properties with a property type have a
structure according to that type's definition, they may have a value
and properties of themselves.
The image on the right displays a schema as represented in the Schema Explorer view. It
allows exploring a schema and inspecting the schema elements. The
top level elements in the tree are types defined in the schema,
their children are the type's properties, their children being the
properties of the properties etc.
See the Schema
elements reference for a detailed explanation on how schema
elements are represented.
