# Package com.saxonica.ee.schema

This package contains classes used to represent the information in a schema, that is, the schema components. The model is closely related to the schema component model defined in the XSD specifications, but not identical in every respect.

Representing the schema itself is the class `PreparedSchema`. All the schemas that have been imported into the application are linked from the `Configuration` object; they thus outlive a single transformation or query. Other important classes have intuitive names, for example ComplexType, SimpleType, ElementDecl, and AttributeDecl.

Schema components in Saxon are always built from schema documents, so the classes representing objects in the schema are constructed using the corresponding classes in the `com.saxonica.schema.sdoc` package. (There is an exception to this: schema components can also be exported to an SCM file, and subsequently re-imported from this file.)

The schema class obtained by the `Configuration.getSuperSchema()` method represents the collection of all loaded schemas. There can only be one active collection of schema components for any one namespace. This means it is not possible to use two unrelated no-namespace schemas concurrently, or two different versions of a schema for the same namespace.

Named types, element declarations, and attribute declarations are indexed directly from the NamePool. It is not necessary first to locate the schema in which they are contained, they can be found directly using the namePool fingerprint of their expanded QName.

The schema model retains nearly all the information in the source schema: the notable omission is annotations.

The API for this package is particular to Saxon, though it is influenced by the definition of schema components in the XSD specification. At some time in the future it is possible that it may be replaced by an API conforming to externally-defined standards.

- Interface Summary
  Interface | Description
  --- | ---
  ComponentReference | A reference to a schema component.
  ComponentWithValueConstraint | Interface for Element Declaration, Attribute Declaration and Attribute Use, created because they share common functionality for handling fixed and default values
  SerializableSchemaComponent | A component that can be serialized by the SchemaSerializer.
  Term | Represents a Term in a content model as defined by XML Schema.
  UserSchemaComponent | A SchemaComponent is an object in a schema.

- Class Summary
  Class | Description
  --- | ---
  AllModelGroup | An AllModelGroup represents an xs:all element in the schema
  Assertion | An Assertion schema component (See XML Schema 1.1 Part 1)
  AssertionFacet | Represents an assertion facet on a schema-defined simple type.
  AttributeDecl | An XML Schema Attribute Declaration.
  AttributeGroupDecl | An XML Schema Attribute Group Declaration.
  AttributeGroupReference | An XML Schema Attribute Group Reference, corresponding to an xs:attributeGroup element with a 'ref' attribute.
  AttributeUse | An XML Schema Attribute Use: that is, a reference to an attribute declaration from within a complex type or attribute group.
  AttributeWildcard | This class represents an xs:anyAttribute element in the schema.
  ChoiceModelGroup | A ChoiceCompositor represents an xs:choice element in the schema
  ContentType | Corresponds to a Content Type Property Record as defined in the XML Schema 1.1 specification
  DigitsFacet | Represents either of the facets totalDigits or fractionDigits
  DistinctFacet | The saxon:distinct facet on a list type can be used to constrain the list to contain distinct values.
  ElementDecl | The object represents an element declaration in the schema.
  ElementParticle | A reference to an element declaration within the content model of a complex type.
  ElementWildcard | This class represents an `<any>` element in the schema.
  EnumerationFacet | Represents a single enumeration facet defined on a simple type.
  EnumerationFacetSet | Represents the set of enumeration values defined on a single simple type, This is a "virtual" facet that combines all the enumeration facets in one simple type definition.
  ExplicitTimezoneFacet | Represents an explicitTimezone facet on a schema-defined simple type derived from date, time, dateTime, gYear, gYearMonth, gMonth, gMonthDay, or gDay
  Facet | Represents an XML Schema Facet.
  FieldOrSelector | The selector of an IdentityConstraint
  FractionDigitsFacet | Represents the fraction-digits facet in a simple type restriction
  IdentityConstraint | The base class for the XML Schema Identity Constraints (key, keyref, unique).
  IdentityConstraintReference | A reference to an identity constraint
  IdentityField | The field selector for an IdentityConstraint
  IdentitySelector | The selector of an IdentityConstraint
  Key | A class that represents the XML Schema Identity Constraint: Key.
  KeyRef | This class represents an xs:keyRef identity constraint in a schema
  LengthFacet | Represents the length facet
  LengthRangeFacet | Abstract class for the three facets length, minLength, and maxLength.
  MaxExclusiveFacet | Implements the maxExclusive facet on a simple type
  MaxInclusiveFacet | Implements the maxInclusive facet on a simple type
  MaxLengthFacet | Represents the minLength facet
  MinExclusiveFacet | Implements the minExclusive facet on a simple type
  MinInclusiveFacet | Implements the minInclusive facet on a simple type
  MinLengthFacet | Represents the minLength facet
  ModelGroup | An XML Schema Model Group.
  ModelGroupDefinition | A Model Group Definition: a schema component corresponding to a top-level (named) xs:group element in a schema document.
  ModelGroupParticle | A reference within the content model of a complex type to a Model Group Definition.
  Notation | A Notation Declaration Schema Component
  OrderFacet | The saxon:order facet on a list type can be used to constrain the list to be in ascending or descending order.
  Particle | Represents a Particle as defined by XML Schema.
  PatternFacet | Represents a pattern facet on a schema-defined simple type
  PreparedSchema | A schema is a collection of schema components.
  PreprocessFacet | Represents the preprocess facet on a schema-defined simple type.
  SchemaCompiler | A SchemaCompiler is capable of reading source schema documents and converting them into collections of schema components.
  SchemaModelLoader | This class allows a compiled schema model in SCM format to be loaded into memory.
  SchemaModelSerializer | This class provides services enabling a compiled schema to be serialized to disk
  SchemaStructure | The base class for all XML Schema stuctures.
  SequenceModelGroup | A SequenceCompositor represents an xs:sequence element in the schema
  SimpleComponentReference | A reference to a named schema group within the content model of a complex type
  SingleNamespaceSchema | A schema (collection of schema components) that has an identifiable target namespace: typically the set of components derived from a single import or include.
  SymbolSpace | This class holds constants used to identify the various symbol spaces defined in XML Schema: element declarations, attribute declarations, types, groups, and so on.
  TotalDigitsFacet | Eepresents the value of the totalDigits facet
  TypeAlternative | A TypeAlternative schema component (See XML Schema 1.1 Part 1 Working Draft)
  TypeReference | A reference to a simple or complex type
  Unique | This class represents an xs:unique identity constraint
  UserAtomicType | An object belonging to this class represents an atomic type: either a built-in atomic type, or a user-defined atomic type.
  UserComplexType | A user-defined complex type (that is, any complex type other than xs:anyType)
  UserDefinedType | This class represents a user-defined simple type or complex type as defined in XML Schema.
  UserListType | Represents a SimpleType that is a list of a given SimpleType, known as its itemType.
  UserSimpleType | This class represents a used-defined simple type, as defined in the XML Schema specification.
  UserUnionType | A class that represents the XML Schema simple-type with variety union.
  ValueConstraint | A value constraint represents the default or fixed value of an element declaration, attribute declaration, or attribute use
  ValueRangeFacet | Represents any of the facets minInclusive, maxInclusive, minExclusive, maxExclusive
  WhitespaceFacet | Represents a whitespace facet on a schema-defined simple type
  Wildcard | A class that represents an XML Schema Wildcard.

- Enum Summary
  Enum | Description
  --- | ---
  Optionality |
  ValueConstraint.Variety |

- Exception Summary
  Exception | Description
  --- | ---
  MissingComponentExceptionImpl | This exception occurs when an attempt is made to dereference a reference from one schema component to another, if the target of the reference cannot be found.