“Beware Premature Certainty – Embracing Ambiguous Requirements” on Iasa Global Blog

You have to measure it to manage it!

Many see ambiguity as antithetical to software requirements. However, as Ruth Malan has observed:

Pick your battles with ambiguity careful. She is a wily foe. Not to be dominated. Rather invited to reveal the clarities we can act on. Make decisions with the understanding that we need to watchful, for our assumptions will, sooner or later, become again tenuous in that fog of ambiguity and uncertainty that change churns up.

See the full post on the Iasa Global Blog (a re-post, originally published here).

Beware Premature Certainty – Embracing Ambiguous Requirements

You have to measure it to manage it!

Many see ambiguity as antithetical to software requirements. However, as Ruth Malan has observed:

Pick your battles with ambiguity careful. She is a wily foe. Not to be dominated. Rather invited to reveal the clarities we can act on. Make decisions with the understanding that we need to watchful, for our assumptions will, sooner or later, become again tenuous in that fog of ambiguity and uncertainty that change churns up.

Premature certainty, locking in too soon to a particular quality of service metric or approach to a functional requirement can cause as many problems as requirements that are too vague. For quality of service, also known as “non-functional”, requirements, this manifests as metrics that lack a basis in reality, metrics that do not account for differing circumstances, and/or metrics that fail to align with their objective. For functional requirements, premature certainty presents as designs masquerading as requirements (specifying “how” instead of “what”) and/or contradictory requirements. For both functional and quality of service requirements, this turns what should be an aid to understanding into an impediment, as well as a source of conflict.

Quality of service requirements are particularly susceptible to this problem. In order to manage quality, metrics must be defined to measure against. Unfortunately, validity of those metrics is not always a priority. Numbers may be pulled from thin air, or worse, marketing materials. Without an understanding of the costs, five 9s availability looks like a no-brainer.

Committing to a metric without understanding the qualitative value of that measure is risky. A three-second response time sounds quick, but will it feel quick? Is it reasonable given the work to be performed? Is it reasonable across the range of environmental conditions that can be expected? How exactly does one measure maintainability? As Tom Graves, in “Metrics for qualitative requirements” noted:

To put it at perhaps its simplest, there’s a qualitative difference between quantitative-requirements and qualitative ones: and the latter cannot and must not be reduced solely to some form of quantitative metric, else the quality that makes it ‘qualitative’ will itself be lost.

In another post, “Requisite Fuzziness”, Tom points out that measures are proxies for qualities, not the qualities themselves. A naive approach can fail to meet the intended objective: “The reality is that whilst vehicle-speed can be measured quite easily, often to a high degree of precision, ‘safe speed’ is highly-variable and highly-contextual.” This context-bound nature begets a concept he refers to as “requisite fuzziness”:

It’s sort-of related to probability, or uncertainty, but it’s not quite the same: more an indicator of how much we need to take that uncertainty into account in system-designs and system-governance. If there’s low requisite-fuzziness in the context, we can use simple metrics and true/false rules to guide decision-making for that context; but if there’s high requisite-fuzziness, any metrics must be interpreted solely as guidance, not as mandatory ‘rules’.

The benefits of requisite fuzziness for functional requirements is somewhat counter-intuitive. Most would argue against ambiguity, as indeed Jeff Sutherland did in “Enabling Specifications: The Key to Building Agile Systems”:

The lawyers pointed out that a patent application is an “enabling specification.” This is a legal term that describes a document that allows the average person knowledgeable in the domain to create the feature without having any discussion with the originators of the enabling specification.

In general, requirements are NOT enabling specifications. On a recent project at a large global company we discovered that hundreds of pages of requirements were not enabling specifications. On the average 60% of what was in the documents was useless to developers. It caused estimates to double in size. Even worse, 10% of what was needed by developers to implement the software was not in the requirements.

The enabling specifications used at PatientKeeper provided a global description of a feature set framed as lightweight user stories with screen shots, business logic, and data structures. The enabling specification was used to generate user stories which then formed the product backlog. The global feature description was updated regularly by the Product Owner team and was a reference to the state of the system that allowed developers to see where the user stories in the product backlog came from.

A user story needes to be a mini-enabling specification for agile teams to operate at peak performance. If it is not, there will be the need for continued dialogue with the Product Owner during the sprint to figure out what the story means. This will reduce story process efficiency and cripple velocity.

While this level of detail may well enable a team to develop efficiently, it may cripple the team’s ability to develop effectively. Given the interdependent relationship between architecture and requirements, overly prescriptive requirements can introduce risk. When design elements (such as “data structures” above) find their way into requirements, it may be that the requirement cannot be implemented as specified within the constraints of the architecture. Without the dialog Jeff referred to, either the requirement will be ignored or the integrity of the architecture will be violated. Neither of these options are advisable.

Another danger inherent in this situation is that of solving the wrong problem. This was addressed by Charlie Alfred in “Invisible Requirements”:

Coming to solutions (requirements) too quickly often times overlooks potentially more beneficial solutions. To illustrate this, consider the Jefferson Memorial.

Several years ago, excessive erosion of the Jefferson Memorial was noticed. A brief investigation identified excessive cleaning as the cause. Since the memorial must be kept clean, more investigation was necessary. Bird droppings were identified as the culprit, so actions were taken to have fewer birds around.Eventually, however, someone asked why the birds were such a problem with the Jefferson Memorial and not the others. Another study determined that the birds frequented the memorial, not for love of Jefferson, but for love of the many tasty spiders that made their home there. Probing further, the spiders were thriving because the insect population was proliferating.Finally, understanding that the insects were attracted by the memorial lights at dusk and dawn identified the ultimate solution. Turn off the lights. Initial solutions driven by quick decisions by memorial managers (i.e. powerful stakeholders) provided expensive ill-suited solutions for an ill-understood problem. The root cause and final solution requirement were well hidden, only brought to light by extensive and time consuming trial and error solutions. Each required solution inappropriately framed the problem, missing the associated hidden causes and final necessary requirement.

“Expensive”, coupled with “extensive and time consuming”, should give pause, particularly when used to describe failures. Naively implementing a set of requirements without technical analysis may well harm the customer. In “Changing Requirements: You Have a Role to Play!”, Raja Bavani noted:

You have to understand what business analysts or product owners provide you. You have to ask questions as early as you can. You have to think in terms of test scenarios and test data. You have to validate your thoughts and assumptions whenever you are in doubt. You have to think about related user stories and conflicting requirements. Instead of doing all these, if you are going to remain a passive consumer of the inputs received from business analysts or product owners, I am sure you are seeding bug issues.

While we don’t want requirements that are deliberately undecipherable, neither can we expect requirements that are both fully developed and cohesive with the architecture as a whole. Rather, we should hope for something like what Robert Galen suggested, that “communicates…goals while leaving the flexibility for my architect to do their job”. They should be, according to J. B. Rainsberger, a ticket to a conversation.

Lisa Crispin captured the reason for this conversation in “Helping the Customer Stick to the Purpose of a User Story”:

Make sure you understand the *purpose* of a user story or feature. Start with the “why”. You can worry later about the “how”. The customers get to decide on the business value to be delivered. They generally aren’t qualified to dictate the technical implementation of that functionality. We, the technical team, get to decide the best way to deliver the desired feature through the software. Always ask about the business problem to be solved. Sometimes, it’s possible to implement a “solution” that doesn’t really solve the problem.

Likewise, Roman Pichler observed:

If I say, for instance, that booking a training course on our website should be quick, then that’s a first step towards describing the attribute. But it would be too vague to characterise the desired user experience, to help the development team make the right architecture choices, and to validate the constraint. I will hence have to iterate over it, which is best done together with the development team.

Rather than passively implementing specifications and hoping that a coherent architecture “emerges”, iteratively refining requirements with those responsible for the architecture stacks the deck in favor of success by surfing ambiguity:

“When you ask a question, what two word answer distinguishes the architect?” And they didn’t miss a beat, answering “It depends” in an instant. “That’s my litmus test for architects.” I told them. “So, how do I tell a good architect?”…I said “They tell you what it depends on.” Yes, “it depends” is a hat tip to multiple simultaneous possibilities and even truths, which is the hallmark of ambiguity (of the kind that shuts down those who are uncomfortable with it). The good architect can sense what the dependencies are, and figure what to resolve and what to live with, to make progress.

Ruth Malan, A Trace in the Sand

What’s driving your architecture?

In a recent post titled “Architectural Drivers”, Davy Brion listed the factors that influence his architectural choices. Additionally, he makes a number of important observations, such as the wisdom of avoiding unnecessary complexity and the fact that there is no absolute “right” or “wrong”, only trade-offs. His efforts inspired me to put together my own list of drivers, several of which are the same or at least related to his. Additionally, I include some discussion of how they affect the architecture of a given system or solution.


Functionality being the first consideration should not come as a surprise since the name of the site is “Form Follows Function”. Are the user interactions task-oriented processes, basic CRUD operations, or a combination of both? Are those interactions real-time, asynchronous, or a mixture? Is the system stand-alone, server-based, peer to peer, or a hybrid? How much, if any, of the desired functionality is available from third party providers?

The requirements that describe the system’s behavior should be a major determinant of the solution’s application architecture, data architecture, and infrastructure architecture. It is important to look at the requirements in a holistic manner. Although those of the current iteration of the current release will be foremost in mind, some thought should be given to those that will be coming later to avoid painting yourself into a corner. It is also important to understand that the functional requirements will also influence many quality of service requirements. For example, the nature of the processes will affect the authorization scheme, the ability to process asynchronously will affect performance and scalability, etc.

Data Profile

The characteristics of the data to be managed will be a major driver of the architecture. Does the system deal with structured data, unstructured data, or a mixture? If the data is structured, does the functionality infer the need for a relational database or one of the NoSQL variants? Is the data sensitive (either wholly or partly), requiring extra security? How many records/documents will the system handle per day? How large are the units of data? Will the volume of data grow linearly or exponentially? Is there a need for archiving or near-line storage? Does the data lend itself to caching, either in whole or in part? Will there be a need to import data from a prior version of the system or from other systems to be replaced by this one?

This driver will have a major impact on the data architecture, infrastructure architecture and application architecture. Additionally, the characteristics of the data will affect a wide range of non-functional requirements: availability, backup requirements, certification, compliance, disaster recovery requirements, performance, response time, scalability, and security.


Who uses/will use a system significantly influences its architecture. Is the system intended for users internal to an organization, its customers, vendors, or some combination of these? Does the system interact directly with users, provide services to other applications, or both? Does the system have to support multiple platforms, either as a host or client (e.g. mobile)? Is accessibility an issue?

The answers to these questions will particularly impact quality of service concerns such as interoperability, portability, security, and usability. Likewise, this aspect is a significant driver of the infrastructure architecture.

Usage Characteristics

Question around how heavily the system will be used are as significant as the issue of who will be using it. Numbers of concurrent users and operation counts will have considerable impact. Another consideration will be the pattern of that usage: business hours versus around the clock. Will it be steady or spiky? If there are spikes, will they occur on a daily, weekly or monthly basis?

This driver will primarily affect quality of service requirements such as performance, response time, and scalability. If the usage pattern is twenty-four hours a day or nearly so, this will also affect maintenance and backup considerations too. The impact on infrastructure architecture is obvious, but it will also drive application and data architecture as well.

Business Priority

The nature of the system in relation to the enterprise, ranging from mission critical to minor, is a key architectural driver. Gartner’s application classes, as described in my previous post “Application Lifecycle Management Revisited”, may be useful in classifying the business priority of a system as well. Time to market can also be a component of this driver, particularly for systems of innovation. The business owner’s tolerance for risk will also fall under this category, with greater tolerance leading to less emphasis on the associated quality of service requirements. A system of innovation with a business owner having a high tolerance for risk will be a good candidate for quickly accumulating technical debt.

Business priority will drive application architecture, data architecture, and infrastructure architecture. Non-functional requirements associated with this driver include availability, backup requirements, disaster recovery requirements, maintainability, performance, response time, scalability, security, and supportability.

Regulatory and Legal Obligations

Regulatory and legal compliance can have as wide ranging an impact on application, data and infrastructure architecture as functionality and business priority. The salient feature of this driver, however, is that there will be little flexibility around it. If a regulation applies, then the solution complies (or else). This is not to say that there will be no gray areas with this driver, just that they will generally be questions of whether the system falls under the jurisdiction of a particular law or regulation rather than whether or not to comply if it does. HIPAA and Sarbanes-Oxley (SOX) are but two examples of the myriad potential legal obligations that could apply. Other examples of legal issues include licensing compliance (for both commercial and Open Source components and code), copyright, trademark, and patent issues.

Common quality of service requirements associated with this driver include accessibility, auditability, certification, compliance, and security. This is not to say, however, that others could not be impacted by legal and regulatory obligations.

Architectural Standards

If an enterprise has formal architectural standards, obviously they will affect application, infrastructure, and data architecture, including the full range of non-functional requirements. Absence of formal standards, however, should not be mistaken for absence of constraint. The existing environment (e.g. hardware and operating systems, development team background, support team background, etc.) will act as this type of driver in the absence of formal standards or where such formal standards are ignored.

Non-functional requirements associated with this driver will typically include accessibility, extensibility, maintainability, security, supportability, testability, and usability.

Audit Requirements

Arguably, audit requirements could have been lumped under functionality, but I listed it separately because of the variety of sources that these requirements can come from. Laws, regulations, the organization’s internal auditors, and even the business users may require tracking system activity. Audit information can also be valuable in determining usage volume and patterns, making operations another potential stakeholder for this driver.

Audit requirements will primarily drive application and data architecture. Obviously, auditability is the primary non-functional requirement affected, but performance, response time, scalability, security, and supportability can all be impacted as well.

Reporting Considerations

Like audit requirements, reporting considerations could be considered a sub-topic of functionality. I list it separately, however, because this driver can be both internal and external to the solution. Reporting that is integral to the solution can affect application, data, and infrastructure architecture (e.g. maintaining a dedicated reporting database to offload reports traffic is a common tactic). Enterprise reporting considerations can likewise impact the architecture of the solution, whether because of the need to support ETL jobs or to participate in master data management, as a supplier, consumer, or both.

This driver can impact quality of service requirements such as auditability (in situations where even reads must be logged), availability, backup requirements, performance, response time, scalability, and security.

Dependencies and Integrations

In “Managing Dependencies”, I outlined a number of ways in which the application architecture is affected by dependency management practices (see “Dependency Management – Anti-Patterns as Art from The Daily WTF” for some humorous, but true examples of how poor dependency management can affect architecture). Likewise, “Using Extension Methods for Message Transformation” and “Strict Versioning for Services – Applying the Open/Closed Principle” cover some of the effects of integrations (using services) on application architecture. Integrations and dependencies may also affect infrastructure (e.g. when connections come from systems external to your network or when using file drops) and data architecture (e.g. when using shared databases).

Non-functional requirements potentially impacted by dependencies and integrations include availability, disaster recovery requirements, interoperability, performance, response time, scalability, security, and supportability. Extensibility could also be potentially affected by this driver. A key consideration in the “Using Extension Methods for Message Transformation” and “Strict Versioning for Services – Applying the Open/Closed Principle” posts is structuring the system to avoid situations where two or more teams must conduct parallel development and releases to avoid breaking integrations.

Cost Constraints

I list this driver separate from business priority because it’s a fact of life that funds may be limited, no matter how critical the system may be. Salaries for development and operations staff; licenses for operating systems, database servers, and other dependencies; servers, storage appliances, network hardware and capacity all cost money (and this is far from a comprehensive list). These costs must be accounted for to properly understand their impact on the solution as a whole given that all aspects of the architecture are vulnerable to this driver.

Initial State

While this is the last driver in my list, it is by no means the least. New development may be subject to fewer constraints than changes to existing systems, but it isn’t without issues. Existing architecture can be both a limit to your freedom and also a base to build on.

In my opinion, these twelve drivers provide a framework for making architectural decisions for technology solutions, whether built, bought, or rented. It is important not to infer the importance of any one driver from its position in the list; that ranking will be a function of the priorities of the business owner(s) plus the requirements of the enterprise as a whole. Establishing the priorities will assist in balancing the conflict between favoring the simplest possible solution and providing sufficient flexibility to grow and change as time goes on. Additionally, these drivers provide a framework for ensuring that decisions are driven by need and not fads or dogma.