Archive for the ‘Standards’ Category

Unified Architecture Framework Profile (UAFP): Lost in Translation ?

July 2, 2017

Synopsis

The intent of Unified Architecture Framework Profile (UAFP) is to “provide a Domain Meta-model usable by non UML/SysML tool vendors who may wish to implement the UAF within their own tool and metalanguage.”

Detached Architecture (Víctor Enrich)

But a meta-model trying to federate (instead of bypassing) the languages of tools providers has to climb up the abstraction scale above any domain of concerns, in that case systems architectures. Without direct consideration of the domain, the missing semantic contents has to be reintroduced through stereotypes.

Problems with that scheme appear at two critical junctures:

  • Between languages and meta-models, and the way semantics are introduced.
  • Between environments and systems, and the way abstractions are defined.

Caminao’s modeling paradigm is used to illustrate the alternative strategy, namely the direct stereotyping of systems architectures semantics.

Languages vs Stereotypes

Meta-Models are models of models: just like artifacts of the latter represent sets of instances from targeted domains, artifacts of the former represent sets of symbolic artifacts from the latter. So while set higher on the abstraction scale, meta-models still reflect the domain of concerns.

Meta-models takes a higher view of domains, meta-languages don’t.

Things are more complex for languages because linguistic constructs ( syntax and semantics) and pragmatic are meant to be defined independently of domain of discourse. Taking a simple example from the model above, it contains two kinds of relationships:

  • Linguistic constructs:  represents, between actual items and their symbolic counterparts; and inherits, between symbolic descriptions.
  • Domain specific: played by, operates, and supervises.

While meta-models can take into account both categories, that’s not the case for languages which only consider linguistic constructs and mechanisms. Stereotypes often appear as a painless way to span the semantic fault between what meta-models have to do and what languages use to do; but that is misguided because mixing domain specific semantics with language constructs can only breed confusion.

Stereotypes & Semantics

If profiles and stereotypes are meant to refine semantics along domains specifics, trying to conciliate UML/SysML languages and non UML/SysML models puts UAFP in a lopsided position by looking the other way, i.e towards one-fits-all meta-language instead of systems architecture semantics. Its way out of this conundrum is to combine stereotypes with UML constraint, as can be illustrated with PropertySet:

UAFP for PropertySet (italics are for abstract)

Behind the mixing of meta-modeling levels (class, classifier, meta-class, stereotype, meta-constraint) and the jumble of joint modeling concerns (property, measurement, condition), the PropertySet description suggests the overlapping of two different kinds of semantics, one looking at objects and behaviors identified in environments (e.g asset, capability, resource); the other focused on systems components (property, condition, measurement). But using stereotypes indifferently for both kind of semantics has consequences.

Stereotypes, while being the basic UML extension mechanism, comes without much formalism and can be applied extensively. As a corollary, their semantics must be clearly defined in line with the context of their use, in particular for meta-languages topping different contexts.

PropertySet for example is defined as an abstract element equivalent to a data type, simple or structured, a straightforward semantic that can be applied consistently for contexts, domains or languages.

That’s not the case for ActualPropertySet which is defined as an InstanceSpecification for a “set or collection of actual properties”. But properties defined for domains (as opposed to languages) have no instances of their own and can only occur as concrete states of objects, behaviors, or expectations, or as abstract ranges in conditions or constraints. And semantics ambiguities are compounded when inheritance is indifferently applied between a motley of stereotypes.

Properties epitomize the problems brought about by confusing language and domain stereotypes and point to a solution.

To begin with syntax, stereotypes are redundant because properties can be described with well-known language constructs.

As for semantics, stereotyped properties should meet clearly defined purposes; as far as systems architectures are concerned, that would be the mapping to architecture capabilities:

Property must be stereotyped with regard to induced architecture capabilities.

  • Properties that can be directly and immediately processed, symbolic (literal) or not (binary objects).
  • Properties whose processing depends on external resource, symbolic (reference) or not (numeric values).

Such stereotypes could be safely used at language level due to the homogeneity of property semantics. That’s not the case for objects and behaviors.

Languages Abstractions & Symbolic Representations

The confusion between language and domain semantics mirrors the one between enterprise and systems, as can be illustrated by UAFP’s understanding of abstraction.

In the context of programming languages, isAbstract applies to descriptions that are not meant to be instantiated: for UAFP “PhysicalResource” isAbstract because it cannot occur except as “NaturalResource” or “ResourceArtifact”, none of them isAbstract.

“isAbstract” has no bearing on horses and carts, only on the meaning of the class PhysicalResource.

Despite the appearances, it must be reminded that such semantics have nothing to do with the nature of resources, only with what can be said about it. In any case the distinction is irrelevant as long as the only semantics considered are confined to specification languages, which is the purpose of the UAFP.

As that’s not true for enterprise architects, confusion is to arise when the modeling Paradigm is extended as to include environments and their association with systems. Then, not only that two kinds of instances (and therefore abstractions) are to be described, but that the relationship between external and internal instances is to determine systems architectures capabilities. Extending the simple example above:

  • Overlooking the distinction between active and passive physical resources prevents a clear and reliable mapping to architecture technical capabilities.
  • Organizational resource lumps together collective (organization), individual and physical (person), individual and organizational (role), symbolic (responsibility), resources. But these distinctions have a direct consequences for architecture functional capabilities.

Abstraction & Symbolic representation

Hence the importance of the distinction between domain and language semantics, the former for the capabilities of the systems under consideration, the latter for the capabilities of the specification languages.

Systems Never Walk Alone

Profiles are supposed to be handy, reliable, and effective guides for the management of specific domains, in that case the modeling of enterprise architectures. As it happens, the UAF profile seems to set out the other way, forsaking architects’ concerns for tools providers’ ones; that can be seen as a lose-lose venture because:

  • There isn’t much for enterprise architects along that path.
  • Tools interoperability would be better served by a parser focused on languages semantics independently of domain specifics.

Hopefully, new thinking about architecture frameworks (e.g DoDAF) tends to restyle them as EA profiles, which may help to reinstate basic requirements:

  • Explicit modeling of environment, enterprise, and systems.
  • Clear distinction between domain (enterprise and systems architecture) and languages.
  • Unambiguous stereotypes with clear purposes

A simple profile for enterprise architecture

On a broader perspective such a profile would help with the alignment of purposes (enterprise architects vs tools providers), scope (enterprise vs systems), and languages (modeling vs programming).

Further Reading

Models
Architectures
Enterprise Architecture
UML

External Links

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NIEM & Information Exchanges

January 24, 2017

Preamble

The objective of the National Information Exchange Model (NIEM) is to provide a “dictionary of agreed-upon terms, definitions, relationships, and formats that are independent of how information is stored in individual systems.”

(Alfred Jensen)

NIEM’s model makes no difference between data and information (Alfred Jensen)

For that purpose NIEM’s model combines commonly agreed core elements with community-specific ones. Weighted against the benefits of simplicity, this architecture overlooks critical distinctions:

  • Inputs: Data vs Information
  • Dictionary: Lexicon and Thesaurus
  • Meanings: Lexical Items and Semantics
  • Usage: Roots and Aspects

That shallow understanding of information significantly hinders the exchange of information between business or institutional entities across overlapping domains.

Inputs: Data vs Information

Data is made of unprocessed observations, information makes sense of data, and knowledge makes use of information. Given that NIEM is meant to be an exchange between business or institutional users, it should have no concern with data mining or knowledge management.

Data is meaningless, information meaning is set by semantic domains.

As an exchange, NIEM should have no concern with data mining or knowledge management.

The problem is that, as conveyed by “core of data elements that are commonly understood and defined across domains, such as person, activity, document, location”, NIEM’s model makes no explicit distinction between data and information.

As a corollary, it implies that data may not only be meaningful, but universally so, which leads to a critical trap: as substantiated by data analytics, data is not supposed to mean anything before processed into information; to keep with examples, even if the definition of persons and locations may not be specific, the semantics of associated information is nonetheless set by domains, institutional, regulatory, contractual, or otherwise.

Data is meaningless, information meaning is set by semantic domains.

Data is meaningless, information meaning is set by semantic domains.

Not surprisingly, that medley of data and information is mirrored by NIEM’s dictionary.

Dictionary: Lexicon & Thesaurus

As far as languages are concerned, words (e.g “word”, “ξ∏¥” ,”01100″) remain data items until associated to some meaning. For that reason dictionaries are built on different levels, first among them lexical and semantic ones:

  • Lexicons take items on their words and gives each of them a self-contained meaning.
  • Thesauruses position meanings within overlapping galaxies of understandings held together by the semantic equivalent of gravitational forces; the meaning of words can then be weighted by the combined semantic gravity of neighbors.

In line with its shallow understanding of information, NIEM’s dictionary only caters for a lexicon of core standalone items associated with type descriptions to be directly implemented by information systems. But due to the absence of thesaurus, the dictionary cannot tackle the semantics of overlapping domains: if lexicons alone can deal with one-to-one mappings of items to meanings (a), thesauruses are necessary for shared (b) or alternative (c) mappings.

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Shared or alternative meanings cannot be managed with lexicons

With regard to shared mappings (b), distinct lexical items (e.g qualification) have to be mapped to the same entity (e.g person). Whereas some shared features (e.g person’s birth date) can be unequivocally understood across domains, most are set through shared (professional qualification), institutional (university diploma), or specific (enterprise course) domains .

Conversely, alternative mappings (c) arise when the same lexical items (e.g “mole”) can be interpreted differently depending on context (e.g plastic surgeon, farmer, or secret service).

Whereas lexicons may be sufficient for the use of lexical items across domains (namespaces in NIEM parlance), thesauruses are necessary if meanings (as opposed to uses) are to be set across domains. But thesauruses being just tools are not sufficient by themselves to deal with overlapping semantics. That can only be achieved through a conceptual distinction between lexical and semantic envelops.

Meanings: Lexical Items & Semantics

NIEM’s dictionary organize names depending on namespaces and relationships:

  • Namespaces: core (e.g Person) or specific (e.g Subject/Justice).
  • Relationships: types (Counselor/Person) or properties (e.g PersonBirthDate).
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NIEM’s Lexicon: Core (a) and specific (b) and associated core (c) and specific (d) properties

But since lexicons know only names, the organization is not orthogonal, with lexical items mapped indifferently to types and properties. The result being that, deprived of reasoned guidelines, lexical items are chartered arbitrarily, e.g:

Based on core PersonType, the Justice namespace uses three different schemes to define similar lexical items:

  • “Counselor” is described with core PersonType.
  • “Subject” and “Suspect” are both described with specific SubjectType, itself a sub-type of PersonType.
  • “Arrestee” is described with specific ArresteeType, itself a sub-type of SubjectType.

Based on core EntityType:

  • The Human Services namespace bypasses core’s namesake and introduces instead its own specific EmployerType.
  • The Biometrics namespace bypasses possibly overlapping core Measurer and BinaryCaptured and directly uses core EntityType.
Lexical items are meshed disregarding semantics

Lexical items are chartered arbitrarily

Lest expanding lexical items clutter up dictionary semantics, some rules have to be introduced; yet, as noted above, these rules should be limited to information exchange and stop short of knowledge management.

Usage: Roots and Aspects

As far as information exchange is concerned, dictionaries have to deal with lexical and semantic meanings without encroaching on ontologies or knowledge representation. In practice that can be best achieved with dictionaries organized around roots and aspects:

  • Roots and structures (regular, black triangles) are used to anchor information units to business environments, source or destination.
  • Aspects (italics, white triangles) are used to describe how information units are understood and used within business environments.
nformation exchanges are best supported by dictionaries organized around roots and aspects

Information exchanges are best supported by dictionaries organized around roots and aspects

As it happens that distinction can be neatly mapped to core concepts of software engineering.

Further Reading

External Links

Zebras cannot be saddled or harnessed

September 23, 2016

As far as standards go, the more they are, the less they’re worth.

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Read my code, if you can …

What have we got

Assuming that modeling languages are meant to build abstractions, one would expect their respective ladders converging somewhere up in some conceptual or meta cloud.

Assuming that standards are meant to introduce similarities into diversity, one would expect clear-cut taxonomies to be applied to artifacts designs.

Instead one will find bounty of committees, bloated specifications, and an open-minded if clumsy language confronted to a number of specific ones.

What is missing

Given the constitutive role of mathematical logic in computing systems, its quasi absence in modeling methods of their functional behavior is dumbfounding. Formal logic, set theory, semiotics, name it, every aspect of systems modeling can rely on a well established corpus of concepts and constructs. And yet, these scientific assets may be used in labs for research purposes but they remain overlooked for any practical use; as if the laser technology had been kept out of consumers markets for almost a century.

What should be done

The current state of affairs can be illustrated by a Horse vs Zebra metaphor: the former with a long and proved track record of varied, effective and practical usages, the latter with almost nothing to its credit except its archetypal idiosyncrasy.

Like horses, logic can be harnessed or saddled to serve a wide range of purposes without loosing anything of its universality. By contrast, concurrent standards and modeling languages can be likened to zebras: they may be of some use for their owner, but from an outward perspective, what remains is their distinctive stripes.

So the way out of the conundrum seems obvious: get rid of the stripes and put back the harness of logic on all the modeling horses.

Further Readings