SOA: Minimal Functional Requirements

Attempting to enumerate minimal set of template functional items to be addressed for use as "Semantic Signifiers" withing the SOA (Services Oriented Architecture) SIG "Resource Locator and Update Service" specficiation.

Authorship and custodianship metadata that is not directly supporting structural and semantic definition has been removed. Would like to bring in more requirements only as deemed necessary. This does not attempt to meet template repository requirements which would include more details with respect to participants in the management and production of the template.

Metadata supporting publishing status and participants is also not included, it is assumed the availability of templates for use is controlled by a publishing process which may include validation, drafts, deprecation etc. This is not examined here.

SOA: Semantic Signifiers - HL7 Profile Functional Specification

Introduction

This document describes the functional requirements of HL7 templates to support service oriented architecture specification usage. This enables definitions of constraints to content within a HL7 operating profile for a service.

HL7 V3 can represent a template in the form of a LIM - Localized Information Model. It is strictly a serializable message model that is a valid constraint on a CIM - Constrained Information Model. CIMs define message structure and semantics that may be sent over the wire using the XML implementation technology specification, this includes the naming of the XML tags. LIMs are implented as constraints on this wire protocol and can define further restrictions on content allowed.

MIF is the "Model Interchange Format" it is a HL7 artifact formalism for describing all modelling performed in HL7 v3. It is implemented as a set of XML schemas. "mifStaticModelSerialized.xsd" - specfically supports serializable LIM definition. The support for the stated general templating requirements by the MIF is examined here.

The default namespace for this mif schema is "urn:hl7-org:v3/mif" this is assumed in the XPath expressions shown.

Identification

This section describes functional requirement items that support identification of the template instance explicitly or by discovery of for desired semantics

Identifier

An identifier must be bound to templates. This allows reference to a given template from other templates.

MIF Implementation

/serializedStaticModels/serializedStaticModel/@name

The model name is unique within the HL7 organization, this would need to be HL7 namespaced for use as a globally unique identifier.

Name

This may be defined to provide an indication of semantics.

MIF Implementation

/serializedStaticModels/serializedStaticModel/@title

Semantics Description

This is a description of the semantics that may be inferred when this template is invoked. It will aid in determining whether the semantics are suitable for use in a desired context.

MIF Implementation

/serializedStaticModels/serializedStaticModel/annotations/description

Version

This is an indication of the current revision of the template. Versions of a template require that there are no semantic differences to be considered the same template.

MIF Implementation

/serializedStaticModels/serializedStaticModel/history/@id

Classification

Terminology concept terms or free text terms may be bound to the template. This may provide an indication of the content of the constraint statement.

MIF Implementation

/serializedStaticModels/serializedStaticModel/header/@subject

Constraint

This section describes functional requirement items that support constraining a reference model definition. This allows the statement of instatiation constraints that are to be applied when conforming to a template defintion.

Identifier

An identifier may be bound to constraint statements within the template. This allows reference to any part of the constraint hierarchy that can be identified.

MIF Implementation

//class/@name

Within the scope of a given template each class is uniquely named and can thus be identified.

Reference Model Derivation

The reference model class that is being constrained must be identified.

MIF Implementation

It is assumed the base reference model is the RIM. By definition a LIM is a constraint of a CIM, and a CIM a constraint of a DIM, and a DIM a constraint on the RIM. The entire constraint hierarchy can be found. With each class in the CIM/DIM/RIM hierarchy named the:

//class/derivationSupplier/@name

Dependencies are ordered by:

//class/derivationSupplier/@staticModelDerivationId

This defines which base class in the reference model is being constrained by the class defintion in the template.

Explicit Attribute Constraints

Constraint statements can be made on attributes of a reference model. This allows the definition of which attributes are allowed to exist in instantiations based on the template.

MIF Implementation

Defintions of attributes that are allowed to exist in instantiations of the parent class based on the template:

//class/attribute

Name of the attribute:

//class/attribute/@name

Source of attribute in the reference model, complete derivation hierarchy:

//class/attribute/derivationSupplier

Each class that is allowed to be instantiated defines which attributes it contains. Since the HL7 methodology requires derived models to be restrictions of the RIM any attributes that do not appear in the defintions (as defiend in the RIM base class) are thus constrained to be not allowed to be instantiated.

Attribute Multiplicity

HL7 v3 attributes are explicitly constraints on the available RIM attributes. The allowed multipliciy range of instances allowed of a specified attribute, this may be:

• 0..1 - optional
• 1..1 - required exactly one instance
• 0..* - unbound collection
• 1..* - unbound collection, required instance
• 0..N - fixed maximum size collection
• 1..N - fixed maximum size collection, required instance

This must be equal to or within the multiplicity of the reference model being constrained.

MIF Implementation

The minimum number of allowed instatiations of the attribute:

//class/attribute/@minimumMultiplicity

The maximum number of allowed instatiations of the attribute:

//class/attribute/@maximumMultiplicity

Collection Type

Defines the type of collection that may be instansiated sorted list, unsorted list, set. This applies to attributes that have a multiplicity that is greater than one.

MIF Implementation

Definition of a collection type:

//class/attribute/type/@name = SET | BAG | LIST

Definition of collection contents type:

//class/attribute/type/supplierBindingArgumentDatatype/@name e.g. CD, ST

Explicit Association Constraints

Constraint statements can be made on associations between classes in the reference model. This allows the definition of which associations are allowed to exist in instantiations based on the template.

MIF Implementation

Defintion of an association between classes, the RIM defines the RIM classes that may be connected with an association, template association definitions determine which associations are allowed to be instantiated when conforming to the template.

//class/association

Association Multiplicity

The HL7 v3 associations are explicitly constraints on the available HL7 RIM associations.

he allowed multipliciy range of instances allowed of a specified association, this may be:

• 0..1 - optional
• 1..1 - required exactly one instance
• 0..* - optional, unbound number of instances
• 1..* - require at least one instance
• 0..N - fixed maximum size
• 1..N - fixed maximum size collection, required instance

This must be equal to or within the multiplicity of the reference model being constrained.

MIF Implementation

The minimum number of allowed instatiations of an association:

//class/association/targetConnection/@minimumMultiplicity

The maximum number of allowed instatiations of an association:

//class/association/targetConnection/@maximumMultiplicity

Instantiation Conditions

Conditional statement defining the inclusion conditions of explicitly defined constraints or referenced templates. This may include reference to environmental variables and to instance values that are within the context of a given template.

Referenced

Reference to identified template to include specified constraints defined in another template.

MIF Implementation

This is implemented in the MIF by CMET references.

Choice

Statement of choice of a number of possible distinct explicitly defined constraints or referenced templates.

MIF Implementation

To implement a choice between classes an abstract base class (or interface) is defined, this defines the allowed (child) specializations. The specialization classes may be explicitly defined in the template or externally reference (CMET).

Instantiation Criteria

Statement of criteria of allowed or exclusion properties of referenced templates not identified directly.

Data Value Constraints

Data value constraints are specific constraints that support common ways of constraining specific data value types. In the HL7 profile this includes all HL7 datatypes?? Or are HL7 v3 datatypes part of the reference model?

Type

Specify the allowed data type that can be instantiated. In the HL7 profile this is defined by the HL7 v3 Datatypes?? Or if the HL7 datatypes are part of the reference model then what are the constrainable datatypes? xsd types? ocl types? ISO?

Range

Numeric range specification, supporting inclusive and exclusive ranges also single and double sided ranges. This may be a range of numeric types or physical quantitiy types.

Measurement Units

This constrains measurement units to a value set that is allowed. This applies to physical quantities.

Code System

This constrains the code system to an allowed set of code system identifiers. This applies to the coded value types.

Value Set

Includes assumed (default) values, fixed values and enumerations for string and coded value types.

Regular Expression

Defines allowed string patterns and applied to string types.

Identifier Root

This constrains the root of an identifier to an allowed set of identifier root values. This applies to identifier types.

Assertions

Stated assertions defining allowed instantiation constraints of values. This may depend on environment variables or other instantiated values within the context of the given template.