EA: The Matter of Layers

As the world turns digital,traditional fences between social, businesses, and systems realms are progressively crumbling. That brings new challenges for enterprises governance, in particular when manifold business stakes and IT systems are concerned.

Layers & labels (T. Cragg)

Supposedly, enterprise architecture would deal with the framing of enterprises and systems concerns into a single paradigm. Yet spirited controversies persist between bottom up and top down approaches, the former trying to upgrade the footprint of IT systems to enterprise level, the latter ready to downgrade these systems to equipment level. But dissent in that case means unfinished business: like diggers tunneling from opposite directions, both groups are to succeed together or fail together. For that to be achieved common sense dictates that both teams agree on target, with each one getting its specific orientation right.

What to look for

Issue (information systems) and circumstances (digitization of business environment) put the focus on the relationship between business processes and enterprises organization and how to capture, manage, and use information.

On that account, and not surprisingly, understandings differ between EA proponents:

  • Bottom-up approaches are focused on the distinction between processes, applications, and data, overlooking key enterprise architecture concerns (a).
  • Top-down approaches come with a better understanding of EA stakes but fall short of the conceptual bridge between organization and business environments (b) .
Bottom-up (a) and top-down (b) approaches to EA

These shortcomings can be mended and approaches made to converge.

How to get there

As already noted, EA can only succeed as a discipline if systems and enterprise perspectives can be crossed, i.e if bottom-up and top-down approaches can be joined. That cannot be achieved along the outdated Process/Application/Data layers:

To begin with, the distinction between application and data, inherited from traditional programming, goes against both object-oriented design and service oriented architectures; then, processes don’t describe architectures but the way they are used.

On a broader perspective, if the impact of digitized business environments on EA is to be taken into account, data and information are to be redefined in a new paradigm, the former associated with a raw input, to be mined from the business environment and processed into the latter. It ensues that (1) data becomes irrelevant for architecture concerns and, (2) information becomes a key asset for enterprise architecture.

Merging applications and data into a logical/functional layer between business and engineering processes also critically redefines the perspective: instead of a being a collection of applications, business processes become the nexus of the architecture.

Introducing a functional layer between business and engineering processes

With a bottom-up EA perspective focused on business and engineering processes, a top-down counterpart has to be set from enterprise perspective that would ensure a meeting of minds around business processes.

That can be readily achieved by keeping processes as pivot between business environments and objectives on one side, enterprise organization on the other side:

Processes are the nexus of enterprise and engineering concerns.

Enterprise architects could then focus on the mapping of business functions to services, the alignment of quality of services with architecture capabilities, and the flows of information across the organization.

Why It Matters

A proper understanding of architecture layers is not an academic concern to be overlooked. As a matter of fact, what is at stake is the very practical purpose of EA: display of boxes and arrows or effective handling of the spindle between business processes and architectural assets. Whereas anything will do for the former, the latter cannot be achieved without a principled and effective coupling between enterprise models and systems engineering.

Further Reading

External Links

Focus: Requirements Reuse


Requirements is what to feed engineering processes. As such they are to be presented under a wide range of forms, and nothing should be assumed upfront about forms or semantics.


What is to be reused: Sketches or Models  ? (John Devlin)

Answering the question of reuse therefore depends on what is to be reused, and for what purpose.

Documentation vs Reuse

Until some analysis can be carried out, requirements are best seen as documents;  whether such documents are to be ephemeral or managed would be decided depending on method (agile or phased), contents (business, supporting systems, implementation, or quality of services), or purpose (e.g governance, regulations, etc).

What is to be reused.

Setting apart external conditions, requirements documentation could be justified by:

  • Traceability of decision-making linking initial requests with actual implementation.
  • Acceptance.
  • Maintenance of deliverables during their life-cycle.

Depending on development approaches, documentation could limited to archives (agile development models) or managed as intermediate products (phased development models). In the latter case reuse would entail some formatting of requirements.

The Cases for Requirements Reuse

Assuming that requirements have been properly formatted, e.g as analysis models (with technical ones managed internally at system level), reuse could be justified by changes in business, functional, or quality of services requirements:

  • Business processes are meant to change with opportunities. With requirements available as analysis models, changes would be more easily managed (a) if they could be fine-grained. Business rules are a clear example, but that could also be the case for new features added to business objects.
  • Functional requirements may change even without change of business ones, e.g if new channels and users are introduced addressing existing business functions. In that case reusable business requirements (b) would dispense with a repeat of business analysis.
  • Finally, quality of service could be affected by operational changes like localization, number of users, volumes, or frequency. Adjusting architecture capabilities would be much easier with functional (c) and business (d) requirements properly documented as analysis models.
Cases for Reuse

Along that perspective, requirements reuse appears to revolve around two pivots, documents and analysis models. Ontologies could be used to bind them.

Requirements & Ontologies

Reusing artifacts means using them in contexts or for purposes different of native ones. That may come by design, when specifications can anticipate on shared concerns, or as an afterthought, when initially unexpected similarities are identified later on. In any case, reuse policies have to overcome a twofold difficulty:

  • Visibility: business and functional analysts must be made aware of potential reuse without having to spend too much time on research.
  • Overheads: ensuring transparency, traceability, and consistency checks on requirements (documents or analysis models) cannot be achieved without costs.

Ontologies could help to achieve greater visibility with acceptable overheads by framing requirements with regard to nature (documents or models) and context:

With regard to nature, the critical distinction is between document management and model based engineering systems. When framed as ontologies, the former is to be implemented as thesaurus targeting terms and documents, the latter as ontologies targeting categories specific to organizations and business domains.

Documents, models, and capabilities should be managed separately

With regard to context the objective should be to manage reusable requirements depending on the kind of jurisdiction and stability of categories, e.g:

  • Institutional: Regulatory authority, steady, changes subject to established procedures.
  • Professional: Agreed upon between parties, steady, changes subject to accord.
  • Corporate: Defined by enterprises, changes subject to internal decision-making.
  • Social: Defined by usage, volatile, continuous and informal changes.
  • Personal: Customary, defined by named individuals (e.g research paper).
Combining contexts of reuse with architectures layers (enterprise, systems, platforms) and capabilities (Who,What,How, Where, When).

Combined with artificial intelligence, ontology archetypes could crucially extend the benefits of requirements reuse, notably through the impact of deep learning for visibility.

On a broader perspective requirements should be seen as a source of knowledge, and their reuse managed accordingly.

Further Reading

Alignment: from Empathy to Abstraction


Empathy is commonly defined as the ability to directly share another person’s state of mind: feelings, emotions, understandings, etc. Such concrete aptitude would clearly help business analysts trying to capture users’ requirements; and on a broader perspective it could even contribute to enterprise capability to foretell trends from actual changes in business environment.

vvvvvv (Picasso)
Perceptions and Abstractions (Picasso)

Analysis goes in the opposite direction as it extracts abstract descriptions from concrete requirements, singling out a subset of features to be shared while foregoing the rest. The same process of abstraction being carried out for enterprise business and organisation on one hand,  systems and software architectures on the other hand.

That dual perspective can be used to define alignment with regard to the level under consideration: users, systems, or enterprise.

Requirements & Architectures

Requirements capture can be seen as a transition from spoken to written language, its objective being to write down what users tell about what they are doing or what they want to do. For that purpose analysts are presented with two basic policies: they can anchor requirements around already known business objects or processes, or they can stick to users’ stories, identify new structuring entities, and organize requirements alongside. In any case, and except for standalone applications, the engineering  process is to be carried out along two paths:

  • One concrete for the development of applications, the objective being to meet users’ requirements with regard to business logic and quality of service.
  • The other abstract for requirements analysis, the objective being to identify new business functions and features and consolidate them with those already supporting current business processes.

Those paths are set in orthogonal dimensions as concrete paths connect users’ activities to applications, and abstractions can only be defined between requirements levels.

Concrete (brown) and Abstract (blue) paths of requirements engineering
Concrete (brown) and Abstract (blue) paths of requirements engineering

As business analysts stand at the crossroad, they have to combine empathy when listening to users concerns and expectations, and abstraction when mapping users requirements to systems functionalities and enterprise business processes.

Architectures & Alignments

As it happens, the same reasoning can be extended to the whole of engineering process, with analysis carried out to navigate between abstraction levels of architectures and requirements, and design used for the realization of each requirements level into its corresponding architecture level:

  • Users’ stories (or more precisely corresponding uses cases) are realized by applications.
  • Business functions and features are realized by services (assuming a service oriented architecture), which are meant to be an abstraction of applications.
  • Business processes are realized by enterprise capabilities, which can be seen as an abstraction of services.
How requirements are realized by design at each architecture level
How requirements are realized by design at each architecture level

That matrix can be used to define three types of alignment:

  • At users level the objective is to ensure that applications are consistent with business logic and provide the expected quality of service. That is what requirements traceability is meant to achieve.
  • At system level the objective is to ensure that business functions and features can be directly mapped to systems functionalities. That is what services oriented architectures (SOA) are  meant to achieve.
  • At enterprise level the objective is to ensure that the enterprise capabilities are congruent with its business objectives, i.e that they support its business processes through an effective use of assets. That is what maturity and capability models are meant to achieve.

That makes alignment a concrete endeavor whatever the architecture layer, i.e not only for users and applications, but also for functions and capabilities.

Enterprise Fourth Dimension

Enterprise Architectures can be fully described as a cross between layers (platforms, systems, organization) and processes (business, engineering, operations). But the validity and usefulness of such outlook is contingent on homogeneous and stable semantics:

  • Homogeneous: some conceptual consensus can be sustained across business units.
  • Stable: some continuity and consistency can be achieved for the mapping between business objectives and targeted environments.

Meeting those conditions may become problematic with the growing part played by services and the crumbling of fences between enterprises and their business environment. In that case alignment will have to rely on a fourth conceptual dimension.

Further Readings

Alignment for Dummies


The emergence of Enterprise Architecture as a discipline of its own has put the light on the necessary distinction between actual (aka business) and software (aka system) realms. Yet, despite a profusion of definitions for layers, tiers, levels, views, and other modeling perspectives, what should be a constitutive premise of system engineering remains largely ignored, namely: business and systems concerns are worlds apart and bridging the gap is the main challenge of architects and analysts, whatever their preserve.

(Alignment with Dummies (J. Baldessari)

The consequences of that neglect appear clearly when enterprise architects consider the alignment of systems architectures and capabilities on one hand, with enterprise organization and business processes on the other hand. Looking into the grey zone in between, some approaches will line up models according to their structure, assuming the same semantics on both sides of the divide; others will climb up the abstraction ladder until everything will look alike. Not surprisingly, with the core interrogation (i.e “what is to be aligned ?”) removed from the equation, models will be turned into dummies enabling alignment to be carried out by simple pattern matching.

Models & Views

The abundance of definitions for layers, tiers or levels often masks two different understandings of models:

  • When models are understood as symbolic descriptions of sets of instances, each layer targets a different context with a different concern. That’s the basis of the Model Driven Architecture (MDA) and its distinction between Computation Independent Models (CIMs), Platform Independent Models (PIMs), and Platform Specific Models (PSMs)
  • When models are understood as symbolic descriptions built from different perspectives, all layers targets the same context, each with a different concern. Along that understanding each view is associated to a specific aspect or level of abstraction: processes view, functional view, conceptual view, technical view, etc.

As it happens, many alignment schemes use, implicitly or explicitly, the second understanding without clarifying the underlying assumptions regarding the backbone of artifacts. That neglect is unfortunate because, to be of any significance, views will have to be aligned with regard to those artifacts.

What is to be aligned

From a general perspective, and beyond lexical controversies, alignment has to be managed with regard to two basic scales:

  • Architectures: enterprise (concepts), systems (functionalities), and platforms (technologies).
  • Models: conceptual (business context and organization), analysis (symbolic representations), design (physical implementation).

From a practical point of view, alignment is meant to deal with two main problems: how business processes are supported by systems functionalities, and how those functionalities are to be implemented. Given that the latter can be fully dealt with at system level, the focus can be put on the alignment of business processes and functional architectures.

A naive solution could be to assume services on both processes and systems sides. Yet, the apparent symmetry covers a tautology: while aiming for services oriented architectures on the systems side would be legitimate, if not necessarily realistic, taking for granted that business processes also tally with services would presume some prior alignment, in other words that the problem has already been solved.

The pragmatic and logically correct approach is therefore to map business processes to system functionalities using whatever option is available, models (CIMs vs PIMs), or views (processes vs functions). And that is where the distinction between business and software semantics is critical: assuming the divide can be overlooked, some “shallow” alignment could be carried out directly providing the models can be translated into some generic language; but if the divide is acknowledged a “deep” alignment will have to be supported by a semantics bridge built across.

Shallow Alignment

Just like models are meant to describe sets of instances, meta-models are meant to describe instances of models independently of their respective semantics. Assuming a semantic continuity between business and systems models, meta-models like OMG’s KDM (Knowledge Discovery Meta-model) appear to provide a very practical solution to the alignment problem.

From a practical point of view, one may assume that no model of functional architecture is available because otherwise it would be aligned “by design” and there would be no problem. So something has to be “extracted” from existing software components:

  1. Software (aka design) models are translated into functional architectures.
  2. Models of business processes are made compatible with the generic language used for system models.
  3. Associations are made based on patterns identified on each side.

While the contents of the first and third steps are well defined and understood, that’s not the case for the second step which take for granted the availability of some agreed upon modeling semantics to be applied to both functional architecture and business processes. Unfortunately that assumption is both factually and logically inconsistent:

  • Factually inconsistent: it is denied by the plethora of candidates claiming for the role, often with partial, overlapping, ambiguous, or conflicting semantics.
  • Logically inconsistent: it simply dodges the question (what’s the meaning of alignment between business processes and supporting systems) either by lumping together the semantics of the respective contexts and concerns, or by climbing up the ladder of abstraction until all semantic discrepancies are smoothed out.

Alignments built on that basis are necessarily shallow as they deal with artifacts disregarding of their contents, like dummies in test plans. As a matter of fact the outcome will add nothing to traceability, which may be enough for trivial or standalone processes and applications, but is to be meaningless when applied at architecture level.

Deep Alignment

Compared to the shallow one, deep alignment, instead of assuming a wide but shallow commonwealth, tries to identify the minimal set of architectural concepts needed to describe alignment’s stake. Moreover, and contrary to the meta-modelling approach, the objective is not to find some higher level of abstraction encompassing the whole of models, but more reasonably to isolate the core of architecture concepts and constructs with shared and unambiguous meanings to be used by both business and system analysts.

That approach can be directly set along the MDA framework:

Deep alignment makes a distinction between what is at stake at architecture level (blue), from the specifics of process or domain (green), and design (brown).
  • Contexts descriptions (UML, DSL, BPM, etc) are not meant to distinguish between architectural constructs and specific ones.
  • Computation independent models (CIMs) describe business objects and processes combining core architectural constructs (using a generic language like UML), with specific business ones. The former can be mapped to functional architecture, the latter (e.g rules) directly transformed into design artifacts.
  • Platform independent models (PIMs) describe functional architectures using core constructs and framework stereotypes, possibly enriched with specific artifacts managed separately.
  • Platform specific models (PSMs) can be obtained through transformation from PIMs, generated using specific languages, or refactored from legacy code.

Alignment can so focus on enterprise and systems architectural stakes leaving the specific concerns dealt with separately, making the best of existing languages.

Alignment & Traceability

As mentioned above, comparing alignment with traceability may help to better understand its meaning and purpose.

  • Traceability is meant to deal with links between development artifacts from requirements to software components. Its main objective is to manage changes in software architecture and support decision-making with regard to maintenance and evolution.
  • Alignment is meant to deal with enterprise objectives and systems capabilities. Its main objective is to manage changes in enterprise architecture and support decision-making with regard to organization and systems architecture.


As a concluding remark, reducing alignment to traceability may counteract its very purpose and make it pointless as a tool for enterprise governance.

Further readings