Requirements-Static Model

Static models define the information structures for the data to be shared by HL7 standards. This includes the types of data elements, the constraints on those data elements and the meaning of each element.

Key Constructs

Requirement	There needs to be a mechanism of grouping data elements that are related.
Rationale	Without organization into logical groupings, data elements become hard to manage or interpret. As well, grouping helps to define the semantics of an element by allowing inheritance of semantics from the definition of the group.
Methodology	HL7 uses the object-oriented concept of "class" to group related data elements
MIF	mif-model-staticBase.xsd/ClassBase
OMG Mapping	UML Class

Requirement	There needs to be a mechanism of defining the relationships between groups of related data elements.
Rationale	The semantics of information in a model is often conveyed by the relationships between those elements. For example, the group of elements representing "Person" might be related to the group representing "Lab Result" as the subject, the performer, supervisor, etc.
Methodology	HL7 uses the object-oriented concept of "association" to link related groups of data elements
MIF	mif-model-staticBase.xsd/AssociationBase
OMG Mapping	UML Association

Requirement	When designing a data model, there needs to be a way of allowing choices of different groupings of concepts when constructing an instance.
Rationale	Instances often need to allow for flexibility. For example, an observation might be made by a patient, a healthcare provider or a patient representative. The set of information to be collected would vary in each circumstance and the model must define what each group of data must be as well as indicate that any one of those options is allowed (and only those options are allowed).
Methodology	HL7 uses the idea of "choices". A choice is an abstract class having no attributes with one or more specialization classes. Each specialization represents one of the options within the choice.
MIF	mif-model-staticBase.xsd/ClassGeneralizationBase
OMG Mapping	This could be modeled in the same way in UML, with a stereotype specifically indicating that a choice is being modeled.

Model metadata

Requirement	Models must be able to indicate whether they are serializable or not.
Rationale	The ability to serialize a model instance in a standardized way is essential for transmitting instances via technologies that require serialization (e.g. XML). However, other HL7 models (such as the RIM ) do not need to be serializable. Knowing whether a model is serializable indicates what sorts of things can be done with it.
MIF	mif-model-staticBase.xsd/StaticModelBase/@isSerializable
OMG Mapping	This could be indicated using an HL7 stereotype. Note, however, that all MOF-based models are serializable using XMI.

Requirement	It must be possible to represent one static model as a set of deltas from another static model.
Rationale	The HL7 methodology relies on a premise of constraint where models are constructed based on other "more abstract" models using a process of derivation . Often these models only make a few constraints to the parent model. However, if the parent model is updated, these models need to be updated to remain proper constraints of the parent. By storing only the "changes" from the parent model the amount of maintenance is significantly reduced.
MIF	mif-model-staticDerived.xsd/derivedStaticModel
OMG Mapping

Requirement	Static models need to be able to identify what format they're represented in.
Rationale	A given static model might be represented in its flat or serialized form or as a derived model. Because each of these representations allows different things to be done with it, it's essential to be able to differentiate what a particular representation looks like.
MIF	mif-model-staticBase.xsd/StaticModelBase/@representationKind
OMG Mapping

Requirement	Static models must be able to indicate the type of conformance rules that apply to the model design, specifically around the use of extensions
Rationale	HL7 has three distinct sets of rules for models depending on what context the model is created in. In order to enforce those rules, the context must be known.
Methodology	International: The model is an international standard - no extensions allowed. RealmExtension: Realm specific extensions allowed in the primary namespace. Localization: Non-balloted specification. Extensions allowed, but only in discrete namespaces
MIF	mif-model-staticBase.xsd/StaticModelBase/@conformanceLevel
OMG Mapping	An appropriate HL7 stereotype could have a tag indicating the conformance context.

Requirement	Static models must be able to indicate whether they are intended to be directly used in the construction of instances, or whether they are only intended to be used as design artifacts to aid the creation of other models.
Rationale	High-level models such as the RIM, Domain Information Models, and some CIMs are not intended to be used directly in the construction of instances. They are too abstract to be safely usable. Without a way to distinguish the intended use of the models, they may be mis-used by implementers.
MIF	mif-model-staticBase.xsd/StaticModelBase/@isAbstract
OMG Mapping	An HL7 model stereotype could have a tag for this.

Requirement	Static Models may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Description Usage Constraint Usage Notes Rationale Requirements Design Comments Stability Remarks Walkthrough Appendix Other Annotation Mapping Open Issue Ballot Comment Change Request Deprecation Information
OMG Mapping	An HL7 model stereotype could have tags for these.

Requirement	Static models must be able to be represented graphically and be able to have that graphical representation persisted.
Rationale	Graphical representation has been found essential to enabling quick communication and understanding of model content. I.e. "A picture is worth 1000 words".
MIF	mif-model-staticBase.xsd/StaticModelBase/graphicRepresentation mif-model-staticBase.xsd/StaticModelBase/figure
OMG Mapping	UML is a graphical notation.

Requirement	Static models must be able to identify the other artifacts they are based on.
Rationale	Static models depend on datatypes and vocabulary and potentially interface packages and/or annotation libraries . If someone reviewing a model doesn't have access to the same versions of these artifacts that were consulted in constructing the model, they will not be able to understand the content within the model and may even misinterpret the model.
MIF	mif-model-staticBase.xsd/StaticModelBase/importedDatatypeModelPackage mif-model-staticBase.xsd/StaticModelBase/importedVocabularyModelPackage mif-model-staticBase.xsd/StaticModelBase/importedInterfacePackage mif-model-staticBase.xsd/StaticModelBase/importedAnnotationLibrary
OMG Mapping	UML already provides for importing of packages. However, such importation is necessary only to make names within the imported package visible without qualification -- it is allowable to reference elements within a package without importing it. Nevertheless, stereotyped UML import relationships could be used to represent the above HL7 dependencies.

Requirement	Static models must be able to identify supplemental datatype flavors defined locally.
Rationale	HL7 has the concept of Datatype Flavors . In some circumstances a datatype flavor may be specific to a particular static model rather than being generically defined and applicable to a variety of static models. In these circumstances the flavor needs to be defined within the model that uses it.
MIF	mif-model-staticBase.xsd/StaticModelBase/additionalDatatypeModel
OMG Mapping	UML allows for the modeling of new data types, which could be stereotyped as appropriate for HL7. [This may need further discussion depending on a deeper review of the HL7 Datatype Flavor concept.]

Requirement	Static models must be able to identify supplemental vocabulary information, particularly value sets, defined locally.
Rationale	In some circumstances a valueset or other vocabulary artifact may be specific to a particular static model rather than being generically defined and applicable to a variety of static models. In these circumstances the vocabulary structures may need to be defined within the model that uses them. (The alternative would be having 1..1 supplemental models maintained separately which would be a maintenance nightmare.)
MIF	mif-model-staticBase.xsd/StaticModelBase/additionalVocabularyModel
OMG Mapping	[Depends on the OMG Mapping for vocabulary models.]

Requirement	Static models must be able to document vocabulary constraints or considerations that apply across the entire model.
Rationale	While many HL7 models are constructed in a way that is independent of any particular technology solution, most models make at least some sort of assumptions about the types of technologies that will be used. These assumptions need to be understood by the implementers of the model if the model is to be implemented safely.
MIF	mif-model-staticBase.xsd/StaticModelBase/vocabularyGuidance
OMG Mapping	[Needs a deeper review of the HL7 concept of "vocabulary guidance".]

Requirement	Static models must be able to group classes into named collections based on "subject area".
Rationale	Some models are too large to be easily understood as a whole. Even for those that are understandable, dividing of the model into a set of sub-sections helps to aid in comprehensibility.
MIF	mif-model-staticBase.xsd/StaticModelBase/subjectAreaPackage
OMG Mapping	UML Package [But would a stereotype be appropriate?]

Requirement	Static models need to be able to identify what coded concept they represent.
Rationale	Some static models, generally templates, are constructed to give concrete representation to a clinical concept from one or more code systems. For example, "blood pressure". When a model has been constructed for this purpose, it needs to be able to identify what code(s) it is representing.
MIF	mif-model-staticBase.xsd/StaticModelBase/definitionalCode
OMG Mapping

Entry Points

Requirement	Static models must be able to identify the places where serialization can begin.
Rationale	Most ITSs communicate static model instances in a serialized manner, for example XML. This serialization must be consistent across implementations for interoperability to occur. As well, because models connect together, the order of serialization indicates where models can connect and thus the semantics that can be expressed through the association of a class in the connecting model with the class in the target model. Consistent serialization means a consistent starting point.
Methodology	HL7 models must have at least one entry point. Some models (which are not directly implementable) may have more than one, indicating that there is more than one class within the model that may be the 'focus' of an exchange.
MIF	mif-model-staticFlat.xsd/StaticModel/entryPoint
OMG Mapping	Stereotype on Class.

Requirement	Entry points must have a name
Rationale	Names allow the entry points to be referred to within a model and by humans.
MIF	mif-model-staticFlat.xsd/StaticModel/entryPoint/@name
OMG Mapping	Tagged value on EntryPoint stereotype.

Requirement	Entry points must be able to identify how they're intended to be used
Rationale	Models can be used for a variety of purposes – as wrappers, CMETs, templates, etc. Identifying the intended use of an entry point clarifies for users of the model how the model is intended to be used from that entry point.
MIF	mif-model-staticFlat.xsd/StaticModel/entryPoint/@useKind
OMG Mapping	Tagged value on EntryPoint stereotype.

Requirement	Entry Points may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Description Usage Constraint Usage Notes Rationale Design Comments Stability Remarks Other Annotation Open Issue Ballot Comment Deprecation Information
OMG Mapping	Tagged values on EntryPoint stereotype.

Classes

Requirement	Static models must support referencing of CMETs and Stubs .
Rationale	HL7 models cannot function in a manner that is totally self contained. Models need to be able to reference other models to allow for re-use, componentization and separation of concerns.
MIF	mif-model-staticFlat.xsd/StaticModel/containedClass/commonModelElementRef mif-model-staticFlat.xsd/StaticModel/containedClass/templateParameter
OMG Mapping	Possibly use stereotyped import relationships.

Requirement	Stubs, CMET references and Classes must all have unique names within a model
Rationale	Names allow human reference and also allow explicit reference of the particular class, CMET or stub referenced by an association or entry point.
MIF	mif-model-staticBase.xsd/ClassBase/@name
OMG Mapping	Assuming stubs, CMETs and classes are all modeled as named elements in UML.

Requirement	Classes based on RIM immutable coded attributes must be able to identify their associated structural vocabulary.
Rationale	The RIM uses structural vocabulary to supplement its object hierarchy. Thus knowing the base physical class in the RIM is not sufficient to know the full meaning of a class. In the case of stubs and CMETs, the vocabulary reference identifies the physical class that will be at the root of the referenced model. For classes in the RIM, the vocabulary reference identifies the location within structural vocabulary hierarchy that corresponds to a class in the physical class hierarchy.
MIF	mif-model-staticBase.xsd/ClassBase/definingVocabulary
OMG Mapping	Tagged value on a Class stereotype.

Requirement	Classes must indicate whether their names are considered "locked"
Rationale	HL7 uses a formal naming algorithm to ensure that class names are consistent with the semantics represented by the class. Because of the requirement for class name uniqueness in the model, the addition or removal of classes from a model sometimes results in a change to the names within a model. When this occurs after a model has been implemented, it creates interoperability issues. By marking the names of "old" classes within a model as 'locked', the naming algorithm knows to leave those classes alone, regardless of the addition or removal of classes.
MIF	mif-model-staticBase.xsd/ClassBase/@nameLocked
OMG Mapping	Tagged value on a Class stereotype.

Requirement	Classes derived from the RIM must be able to distinguish whether omitted attributes and associations are prohibited or unconstrained.
Rationale	In models like RMIMs, omitting an attribute present in the RIM class an RMIM class is derived from means that the attribute is not allowed to appear in instances (except potentially as an extension.) However, in some templates, the desire is to only enforce constraints on what elements must appear, not to prohibit the appearance of anything unspecified. Without an indicator as to which approach is desired, the class cannot be correctly implemented
MIF	mif-model-staticBase.xsd/ClassBase/@isComplete
OMG Mapping	Tagged value on a Class stereotype.

Requirement	Classes, CMETs and Stubs may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Definition Usage Constraint Usage Notes Rationale Requirements Design Comments Stability Remarks Other Annotation Mapping Formal Constraint Open Issue Ballot Comment Change Request Deprecation Information
OMG Mapping	Tagged values on a Class stereotype.

Requirement	At a given class within a static model, the model must be able to assert what templates can be applied and what templates are known that might optionally be applied at that location.
Rationale	Templates allow the application of a set of constraints to a model without altering the wire-format of the instance. As such, templates represent re-usable constraints. Rather than copying those constraints into every model where they need to apply, it is easier to just reference the template. This also significantly simplifies the maintenance effort. Listing of optional templates simplifies things for implementers by providing them with a list of optional constraint sets that are known to be appropriate.
MIF	mif-model-staticBase.xsd/ClassBase/templateInfo/requiredTemplateGroup mif-model-staticBase.xsd/ClassBase/templateInfo/supportedTemplate
OMG Mapping	It may be possible to represent an HL7 template as a UML package template containing constraints on the template parameters. However, some HL7-specific stereotyping may also be required to properly apply such a template in the context of a UML model.

Specializations

Requirement	Classes need to be able to identify other classes that they "subsume".
Rationale	The idea of "specialization" is a key concept in object-oriented representations. It allows classes to be extended by more refined versions with additional attributes and/or associations. HL7 uses this in the standard OO sense for the reference model. It also uses this as a mechanism to allow choices within finer-grained models where each leaf-level specialization in the inheritance structure reflects one of the options at run-time
MIF	mif-model-staticFlat.xsd/FlatClass/childClass
OMG Mapping	UML Generalization

Requirement	Specialization relationships need to identify their expected conformance level.
Rationale	As with attributes, associations and datatypes properties, it's possible for variation in whether an implementation will support all possible specializations (choice options) of a class. It's therefore necessary for specifications to identify which specializations must be supported by all implementations and which are optional. It's also necessary for implementation profiles to identify which optional specializations will actually be supported, which will be ignored and which might result in an error if received.
MIF	mif-model-staticFlat.xsd/FlatClass/childClass/@conformance
OMG Mapping	Stereotype on Generalization.

State Machines

Requirement	Classes with state attributes must be able to define their state machines.
Rationale	State machines help define the dynamic behavior of objects instantiating a class. This helps clarify the semantics of a class and also identifies what can be done with it over time.
MIF	mif-model-staticBase.xsd/ClassBase/behavior
OMG Mapping	State machine owned by a class.

Requirement	The state machine must identify the attribute to which the state machine applies.
Rationale	It's hard to use a state machine if you don't know where to convey or find the current state . . .
MIF	mif-model-staticBase.xsd/ClassBase/behavior/@stateAttributeName
OMG Mapping	Tagged value on a StateMachine stereotype.

Requirement	State machines may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Design Comments Stability Remarks Walkthrough Other Annotation Open Issue Ballot Comment Change Request
OMG Mapping	Tagged values on a StateMachine stereotype.

Requirement	The state machine must be able to be represented graphically
Rationale	A diagram of a state machine is much easier to understand than a flat enumeration of states and transitions
MIF	mif-model-staticBase.xsd/ClassBase/behavior/figure
OMG Mapping	State machine diagram.

Requirement	State machines must list the states they contain, including name
Rationale	A state machine doesn't accomplish much if you don't know what the states are
MIF	mif-model-staticBase.xsd/ClassBase/behavior/subState
OMG Mapping	UML state machines contain states.

Requirement	Staes may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Definition Usage Constraint Usage Notes Rationale Requirements Design Comments Stability Remarks Other Annotation Mapping Formal Constraint Open Issue Ballot Comment Change Request Deprecation Information
OMG Mapping	Tagged values on a State stereotype.

Requirement	States must be able to contain sub-states
Rationale	Sometimes a given state can be partitioned into multiple substates and both the superstate and its substates can be of interest in different use-cases
MIF	mif-model-staticBase.xsd/ClassBase/behavior/subState/containedStates
OMG Mapping	UML provides for composite states.

Requirement	State machines must list the state transitions they support, including name
Rationale	A state machine that doesn't permit transitions between the states doesn't accomplish much.
MIF	mif-model-staticBase.xsd/ClassBase/behavior/transition
OMG Mapping	UML state machines contain transitions.

Requirement	State Transitions may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Definition Usage Constraint Usage Notes Rationale Requirements Design Comments Stability Remarks Walkthrough Other Annotation Mapping Open Issue Ballot Comment Change Request Deprecation Information
OMG Mapping	Tagged values on a Transition stereotype.

Attributes

Most requirements for class attributes can be found in the general section on Static model feature requirements

Requirement	Some attributes need to be marked as "immutable"
Rationale	HL7 uses attributes and vocabulary in place of distinct classes to ensure that the reference model can be expressed in a simple way. These attribute values are not changeable and need to be distinguished from others. In addition, immutable attributes may be rendered differently in some Implementation Technology Specifications.
MIF	mif-model-staticBase.xsd/Attribute/@isImmutable
OMG Mapping	Make the attribute read-only.

Requirement	Some attributes need to have supplemental "properties".
Rationale	At the moment, some attributes are flagged with an "isDocumentCharacteristic" property that identifies how those attributes are interpreted. Other properties may be added over time.
MIF	mif-model-staticBase.xsd/Attribute/property
OMG Mapping	Tagged value(s) on a Property stereotype.

Requirement	Class attributes may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Description Usage Constraint Usage Notes Rationale Requirements Design Comments Stability Remarks Other Annotation Mapping Formal Constraint Open Issue Static Example Ballot Comment Change Request Deprecation Information
OMG Mapping	Tagged values on a Property stereotype.

Association Ends

Each association has an end for each class it is connected to that describes how the association is navigated from that class.

Most requirements for class association ends can be found in the general section on Static model feature requirements

Requirement	Associations must indicate whether their names are considered "locked"
Rationale	HL7 uses a formal naming algorithm to ensure that association navigation names are consistent with the semantics represented by the association. Because of the requirement for association traversal name uniqueness within the context of a class, the addition or removal of associations from a class sometimes results in a change to the names of associations connected to a class. When this occurs after a model has been implemented, it creates interoperability issues. By marking the names of "old" associations within a model as 'locked', the naming algorithm knows to leave those classes alone, regardless of the addition or removal of classes and associations.
MIF	mif-model-staticBase.xsd/AssociationEndBase/@nameLocked
OMG Mapping	Tagged value on a Property stereotype. (Association ends are properties in UML.)

Requirement	Associations that recurse must be able to identify limits on the depth of recursion.
Rationale	Just like any other relationship, failure of implementations to be consistent in their expectations on recursion depth can result in interoperability issues. If a sender nests an association 4 deep and the receiver can only handle nesting three levels deep, information will be lost.
MIF	mif-model-staticBase.xsd/AssociationEndBase/@maximumRecursionDepth
OMG Mapping	Tagged value on an Property stereotype. (Or perhaps on Association?)

Requirement	Associations must be able to capture "history" just the same as the HXIT datatype.
Rationale	The HXIT datatype allows a timestamp and linkage to a particular ControlAct to be associated with each repetition of an attribute. This allows for detailed history information of exactly when a part of a model was changed, by whom, why, etc. This same sort of information can need to be captured for associations. And associations must therefore indicate whether that information is allowed or not.
MIF	mif-model-staticBase.xsd/AssociationEndBase/@referenceHistory
OMG Mapping	Tagged values on a Property stereotype.

Requirement	Association ends may have a number of different types of annotations
Rationale	See rationales for individual annotations types
Implementation	Description Usage Constraint Usage Notes Rationale Requirements Design Comments Stability Remarks Other Annotation Mapping Formal Constraint Open Issue Ballot Comment Change Request Deprecation Information
OMG Mapping	Tagged values on a Property stereotype. (Same as the annotations for a property used as an attribute.)

Requirement	When an association points to a choice structure (an abstract class having specializations), it needs to capture traversal names for each of the classes, CMETs and stubs in the choice hierarchy.
Rationale	With some ITSs, such as XML, there's a requirement that traversal names be distinct when the types are distinct. By definition, a choice structure consists of multiple potential types. Each of those types therefore requires a name.
MIF	mif-model-staticBase.xsd/AssociationEndBase/ChoiceItem/@traversalName
OMG Mapping	Perhaps a stereotype on a dependency from the association end to each choice item, with the traversal name as a tagged value.