Archive for May, 2012

Conceptual Architecture: How

How: Some Comments on Creating and Evolving the Conceptual Architecture

During early system conceptualization, we start to envision the form or shape of the system, its boundaries and interactions, its primary elements and their interactions. The sketchy shapes of these elements, expressed mainly in terms of their responsibilities, analogies, and drawing on patterns and experience, take a rough form, allowing us to investigate the system concept. Then, as the system concept (identity, value propositions and capabilities) takes shape, so too does the Conceptual Architecture.

In designing complex systems, separation of concerns is a key strategy for gaining intellectual traction and enabling ourselves to reason about important design decisions while considering cross-cutting concerns that are part and parcel of the decomposition-composition dual of systems design and development. The concerns focused on at this point are related to giving shape to the system paying attention to user-facing capabilities and developer-facing properties of the system. We seek to bring intentionality and experience to design to achieve more the system properties we want, recognizing that ultimately system properties are emergent and we will need to sense and respond and adapt as we learn more from the system in context.

The architectural elements of software systems (that is, elements significant enough to the system to draw out and deal with in architectural design) are constructs of inventive human thought. We mold and shape them to accomplish a purpose, subject to constraints and forces. We leverage analogies to draw experience and knowledge from other domains, including mechanisms of nature (e.g., swarms), man-made (e.g., mechanical mechanisms like hubs), and social constructs (e.g., social and economic mechanisms like brokers).

The Conceptual Architecture Diagram is a lightweight and yet powerful tool for sketch-prototyping the system structure, and for rendering the structure of an existing system, to explore adaptations to it. Thus it allows us to explore the system from its earliest conception through evolution. As we experiment on paper, it is cheap to postulate various alternatives and explore their ramifications.
Early Conceptual Architecture exploration (depicted figuratively)
Later Conceptual Architecture elaboration and documentation

As system capabilities are defined, the associated responsibilities are allocated to “chunks” or components of the system, and these responsibilities are an important thinking tool for architectural designers who need to make software abstractions cognitively malleable and communicable. With something so simple as elements each with their list of responsibilities and relationships, we can experiment with different factorings and hence different abstractions or elements each with a different basis for cohesion of responsibilities. Further, it becomes possible to assess:

  • clarity of responsibilities
  • whether responsibilities are missing
  • components for cohesion of responsibilities
  • the system shape for balanced distribution of responsibilities

Architectural components may play different roles in the system, so their responsibilities are related within role-scopes. That is to say, for example, a component may play a minor role in system health monitoring and an active role with respect to some other system capability (e.g., providing shopping cart functionality). 

In highly dynamic systems, as software intensive systems are, structure and dynamics are designed together — if we focus on structure we impact dynamics, and vice versa. When we focus on dynamics — on behavior and “how it works” and properties that emerge from the structures as they perform their function and interact — our design decisions have to be expressed in terms of the structure for the structure houses, if you like, the implied responsibilities and interfaces.

The conceptualization of a product isn’t limited to the conceptualization of its use, but the product in use. We’re designing what the product is capable of in conjunction with what the product is and how it is built. A car isn’t a faster carriage, and although early cars had aspects of a carriage, the engine was quite different than a horse, and this translated to mechanisms to make the wheels move (from passive to active). In other words, when we conceptualize a new kind of product we iterate across designing capabilities and the mechanisms and structures that deliver those capabilities, and the product changes the ecosystem (a gasoline powered car raises the need for places to replenish fuel) so to make the product successful we also (impact the) redesign (of) key aspects of the ecosystem or larger system of systems into which our system fits, interacts and in important ways shapes and is shaped by.

“In most people’s vocabularies, design means veneer. It’s interior decorating. It’s the fabric of the curtains and the sofa. But to me, nothing could be further from the meaning of design. Design is the fundamental soul of a man-made creation that ends up expressing itself in successive outer layers of the product or service. … The essence of the iMac is to be the finest possible consumer computer in which each element plays together” — Steve Jobs

Conceptual Architecture grants us passage between the from-the-outside and the from-the-inside views of the system, allowing us to design interactively across the concept of the system and the internal concepts that allow that conception to take form. And it allows us to think about the elements and how they play together. More specifically, it is the conception and narration of the organization of the parts or elements of the system and its key, or architecturally significant, mechanisms — as the system is conceived, developed and evolved. More pivotally, it is an agent of consilience, helping us to bridge various divides in system design.

Some related resources and ideas:

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Conceptual Architecture: Why

Why: Motivation for the Conceptual Architecture View

Conceptual Architecture is a key medium for describing the “big picture” and essential design ideas of our system, helping others to more rapidly comprehend a complex system, how it is composed and its critical mechanisms or interworking to achieve some key internal system capability essential to sustaining itself. The Conceptual Architecture Diagram serves as a high level map of our system, providing for navigation around complex systems, location of responsibilities, and identification of dependencies.

But Conceptual Architecture is also a focus of essential design work! As we conceive of the system structure, we’re tackling questions of decomposition and modularity, with the dual of composition and emergent properties. We do so to make the system organizationally and cognitively tractable, bringing order to the system. We might think of this as a kind of “social order” if we see its elements as agents of system responsibilities, working with cohorts to deliver system capabilities and in this interaction effecting emergent properties. But even if we don’t go that far, we are at least bringing a kind of mechanical order, complete with hierarchically composed sub-orders, to the system.

Modular systems enable us to:

  • simplify the design with cohesive units of responsibility
  • partition realms of uncertainty and experiment, separating them from more stable and understood areas of the system;
  • separate areas of the system that change for the same reason (for example, dependencies on underlying technology), from other areas of the system that have different change impulses;
  • create areas of focus for investments in highly tuned performance or extreme robustness and resilience;
  • separate elements for reuse or leverage; and
  • create units of accountability. (Whether we organize development primarily by features or by components, it is helpful to have clear component ownership so that the structural health of the component is an explicit charter.)
  • Early on, we’re dealing with our conceits of formative system elements — on paper. We’re crafting lo-fidelity sketch-prototypes of the system structure, and iterating across the conception of the system and our discovery and exploration of how we might conceive of, arrange and build the system. Because it is cheap to do, relying more on how generative our imagination is leveraging the grist of experience, patterns, capabilities in other systems and frameworks, and so forth, we can explore various alternatives, discovering elements and relationships, illuminating the system conception or possibilities we might offer in terms of system capabilities. We can play with different factorings of responsibilities into capabilities and onto elements. And we can evaluate our postulated alternatives with respect to coverage or completeness as well as balance, harmony, conceptual integrity and consistency, in addition to the achievement of desired system outcomes. All of which allows for a much more active, adaptive, creative exploration of the system concept and structural organization before the direction is channeled and cast in shaping, anchoring expectations and code.

    We don’t claim to be able to so well conceive of the system in its ultimate form that we go into system development with a perfect and complete design. We do claim that we can begin the evolutionary adaptation process with a more plastic and malleable medium than a growing mass of code. And then we can support code evolution with, again, a more malleable medium for exploring architectural-level refactoring and adaptations — changing sketches and more formal models to explore the impact of ideas before we incur the cost of making the changes in the code base. All the while maintaining greater intellectual traction over a complex system, because we have cognitive aids to system understanding and work with system constructs in their own terms, rather than always and only in terms of code which contains details that obfuscate.

    Some related reading:

  • Decisions, Concerns …(re-)Defining Software Architecture
  • Why Do We Need Software Architecture?
  • What architecture is about
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    Conceptual Architecture: What

    What is Conceptual Architecture?

    “Conceptual Architecture” is the conceptual view(s) of the architecture of a system. It describes at a broad brushstrokes conceptual level the significant design ideas of the system. In particular, this view includes diagrams and text which identify, explicate, rationalize and contextualize the key structures and mechanisms of the system, and the relationships among them.

    Conceptual Architecture expresses the key architectural elements and their relationships that give “shape” to the system. Each of these architectural elements, or abstractions, play a critical role in the system which is signified by their responsibility assignments. They collaborate and interact, and these relationships are a significant design consideration not only because interaction points (analogous to articulation points in physical systems) and “seams” in the system are non-trivial, but because interactions give rise to synergy that makes the system more than a simple aggregate of executing parts. The parts, their arrangement and concert, cohere within and give expression to the system “gestalt.”

    Conceptual Architecture Diagram

    The Conceptual Architecture Diagram renders the formative architectural abstractions (named boxes) and their interrelationships (lines). For complex systems, there may be a set of such diagrams, exploring the (de)composition of more complex, architecturally interesting architectural elements.

    Component-Responsibility-Collaborator-Rationale (CRC-R) Descriptions

    The Conceptual Architecture also identifies the responsibilities of each of the architectural elements. We advocate doing this on Component-Responsibility-Collaborator-Rationale (CRC-R) Descriptions* for each (conceptual architecture) component, so that the reasoning behind component design choices is captured along with the responsibilities (connecting the dots to desired outcomes, strategic decisions, lessons from experience and grounding assumptions, etc.), and dependencies and other relationships are also recorded. It is a simple and “just enough” format that matches the spirit and intent of Conceptual Architecture, supporting conception, communication and evolution of the key design ideas, including the fundamental organization, of the system.

    Mechanism Sketches

    Beyond the (set of) Conceptual Architecture Diagram(s) and CRC-R descriptions, architectural mechanisms (i.e., mechanisms of architectural significance) are sketched (in diagrams and descriptions) to conceive and convey their essential design nature — the design intent, contextual assumptions, structure, and “how it works” dynamic considerations. The capabilities of the system emerge from the inter- and intra-working of the parts of the system, and mechanisms allow us to focus on specific processes within the system, conceptually (at this point) designing architecturally significant functions of parts of the system.

    Architecturally significant mechanisms are those that have more diffuse or systemic impact or are make-or-break important to system outcomes. Many of the patterns in our field’s literature formulate tried-and-true mechanism designs addressing very specific system capabilities (often internally focused at system sustaining and structural integrity concerns because these are common across systems irrespective of their specific user-facing functionality). A system has functions just like a body has functions. And many of these are internal system sustaining functions that have to do with continuity rather than serving any immediate external demand being made of the system.

    Together, the expressions of the Conceptual Architecture form a conceptual framework within which we conceive of, reason about, communicate and share, extend and reify and evolve the key design ideas of the system.

    References and More Information

  • Conceptual Architecture [Draft for Review], Ruth Malan
  • Conceptual Architecture and example Conceptual Architecture and Why Bother with Concepts, by Doug Newdick
  • Our draft chapter on Conceptual Architecture (the book has been reconceived and is being rewritten)
  • Key to conceptual architecture is the notion of abstraction. I need to rework it, but this piece on Software Abstractions gives an introduction.
  • Logical Architecture is the actionable set of architectural design descriptions or specifications, and includes interface specification.
  • Context: see Visual Architecting Poster and Core Activities Chart.
  • Conway’s Law and architecture of responsibility
  • The influence here also includes the RDD (responsibility driven design) work of Rebecca Wirfs-Brock, as well as work we were doing on Team Fusion under the leadership of Derek Coleman.
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