Experience with XML Schema Ashok Malhotra

Schema Usage  Mapping XML Schema and XML documents controlled by the Schema to object classes and instances.  Storing XML Schemas and documents in the database.

Mapping XML Schema to Object Classes  Choice  Derivation by Restriction  Facets  Derivation Control  Namespace Restrictions  Problems with Annotations

Mapping XML Schema to Object Classes - Choice  Choice allows variations in the content of an object.  No equivalent construct in Java.  Some languages support variant classes.

Mapping XML Schema to Object Classes  Derivation by restriction has no object- oriented equivalent.  In the database, a restricted type is mapped to a dummy subtype with no additional fields. Restriction not enforced at SQL level.  Similarly, for datatypes, facets have no object-oriented equivalent.  Must be checked at runtime.

Mapping XML Schema to Object Classes – fixed, final, block, etc.  Fixed and final restrict derivation from elements.  Block restricts use of derived types where the parent type is expected.  Only final #all has a Java equivalent.

Mapping XML Schema to Object Classes – wildcard restrictions  Wildcards can be restricted to elements from a specific namespace.  No equivalent object-oriented concept.

Mapping XML Schema to Object Classes – problems with annotations  Can an annotation be added to a “ref” ?  If so, does it take precedence over an annotation of the entity referred to?  We assume annotations can be applied to a ‘ref’, and …  The annotation element on an attribute ref is associated with {Attribute Use}.  The annotation element on a model group ref or an element ref is associated with the {particle}.

Managing XML Schemas and documents in the database  Support is provided for the following tasks: – Registering XML Schemas. – Validating XML documents against a registered XML Schema. – Generating XML Schema from object classes. – Generating a structured database mapping from XML Schemas during XML Schema registration. This includes generating SQL object types, collection types, and default tables, and capturing the mapping information using special attributes. – Performing manipulation (DML) and queries on XML Schema-based XMLType tables. – Automatically inserting data into default tables when schema-based XML instances are inserted into Oracle XML DB repository using FTP, HTTP/WebDAV protocols and other languages.

Managing XML Schemas and documents in the database – Substitution groups  Instance data is stored in a column/table corresponding to the head element.  Additional information includes the actual element type.  Also includes, namespace prefixes, comments, PIs.

Managing XML Schemas and documents in the database – non-SQL datatypes  Datatypes that cannot be represented in SQL are mapped to a VARCHAR2 column.  This is also on option for datatypes that do map cleanly to SQL types e.g. integer.  Schema annotation can be used to specify storage option.

Managing XML Schemas and documents in the database – key/keyref  Not enforced at SQL level but at the XML level.  Key/keyref apply within a document whereas, in most cases, such constraints are useful over a document collection.

Managing XML Schemas and documents in the database – wildcard with namespace exclusion  Cannot define a wildcard that allows elements not in a specified namespace and also allows the null namespace.  Needed to add proprietary extensions to handle this case.

Managing XML Schemas and documents in the database – redefine  Redefine is the only XML Schema feature not supported.  No customer has asked for this, yet!