5. Aufgabe (a)
Erläutern Sie die Begriffe schema component, ur-type, particle, initial value, normalized value, assessment, strict assessment, lax assessment, valid restriction sowie PSVI im Zusammenhang mit XML Schema.
Schema components are building blocks of which the schema consists, namely: element and attribute declarations, simple and complex type definitions; attribute group definitions, model group definitions, identity-constrain definitions and notation declarations; annotations, wildcards, model groups, particles and attribute users.
Information item is an abstract representation of some part of an XML document (it can be, for instance, element declaration). Information items form together the XML document Information set or Infoset. Validation is a relation between information items and schema components.
Ur-type is either (1) a complex type definition present in each XML schema that serves as a root in the type definition hierarchy and is referred to as “anyType” in XML schema namespace or (2) a simple type definition, which is a restriction of ur-type definition (is referred to as “anySimpleType”) and has unconstrained lexical space (?), and its value space is composed of the union of all build-in primitive datatypes value spaces. The mapping from lexical space to value space is unspecified for the items of the second type.
Particle is a term for element content, consisting of either an element declaration, a wildcard or a model group, together with occurrence constraints.
Initial value, normalized value:
The initial value of an element information item is the string composed of the [character code] of each character information item in the [children] of that element information item; normalized value of an element or attribute information item is an initial value whose white space, if any, has been normalized according to the value of the whiteSpace facet of the simple type definition used in its validation.
The term absent is used as a distinguished property value denoting absence, in other words absent element = there's no element.
Context-determined declarations - associations established during validation between the elements /attributes information items among the [children] and [attributes] on the one hand, and element and attribute declarations on the other. The term [children] here denotes the ordered list of information items consisting of element, processing instruction, unexpanded entity reference, character, and comment information items, one for each element, processing instruction, reference to an unprocessed external entity, data character, and comment appearing immediately within the current element. If the element is empty, this list has no members. The term [attributes] denotes an ordered list of all attribute information items of a specific element (without namespace declarations)
Assessment is the process of determining whether all of the information items comply with the restrictions stated in the corresponding Schema components and changing the XML document infoset in accordance to the Schema (as a result it becomes PSVI).
Strict assessment the element information item is said to be strictly assessed if the following conditions hold: (1.1) there is a known declaration for the non-absent element and (1.2) a known definition for the non-absent types and they both are valid; (2) the schema validity of both the element and attribute information items has been assessed.
Lax assessment if neither clause 1.1 nor 1.2 are satisfied and its context-determined declaration is not skip by validating with respect to the ur-type definition, the element information item is said to be laxly assessed.
PSVI stands for post-schema-validation Infoset. It is acquired from the original XML document infoset by bringing it in accordance to the constrains imposed on XML document by the corresponding Schema, which can include assigning default values to the attributes, normalizing element and attribute values, etc.
Valid restriction is a restriction of either simple or complex type for which Derivation constrain holds.
Derivation constraint for simple type
For a simple type definition (call it D, for derived) to be validly derived from a type definition (call this B, for base) given a subset of {extension, restriction, list, union} (of which only restriction is actually relevant) the following conditions must hold: they are (1) either the same type definition or (2.1) restriction is not in the subset and either (2.2) D's base type is B, or D's base type is not the ur-type and is validly derived from B given the subset, D's [variety] is list or union and B is the simple ur-type definition, B's variety is union and D is validly derived from a type definition in B's.
The term [variety] stands for either atomic (a built-in primitive simple type definition), list (a simple type definition) or union ( a non-empty sequence of simple type definitions).
Derivation constraint for complex type
the base type should be a complex type without a restriction, it should also be the ur-type definition, it can be either element-only or mixed; the content type of the complex type definition must be empty; the required attrbitutes for the base type must also be required for the complex type definition; the particle of the complex type definition must be a valid restriction of the particle of the base-type.
