Are They Really Requirements?

The paradigm we get from the waterfall model is that a client states their requirements and they lead unidirectionally to the specification for the system. We already know from the popularity of the Agile methods that waterfall is not the correct model, that for many projects it is more productive to approach it as an artistic product and make many iterations that can be shared with the client. The benefits of this approach have been well documented but it still leaves the idea that there are some set of requirements that just need to be uncovered and refined. I now believe this is a fatal flaw in this part of even the Agile methods.

Iterative methods gain their power from the inclusion of the client in the design process. In the older waterfall approaches, after the requirements were documented and signed off, the client would often see little progress (except bills and excuses why the project was behind schedule) until an advanced level of testing allowed the client to see the complete system as it is intended to work. The pain this caused when it was realized that what was built was not an acceptable solution to the client's problem was always significant since so much had already been sunk into the wrong solution. Agile at least boxes the risk into a single iteration and if they are small enough, the damage can be limited. One good trait of all these Agile methods is that they support faster failure of dysfunctional projects.

Clients have always had misgivings about requirements signoffs. While they could not articulate it, they felt they were being setup for failure. Their business expertise did not prepare them for the task of directly specifying the product they needed nor is the average business analyst prepared to completely understand the business function that is within the scope of development. Neither is generally prepared for the design tradeoffs that are often done without any direct client involvement, even if the team is articulate enough to explain how a particular design decision impacts the various emergent properties of the system under construction. The current methodologies simply don't work during the requirements elicitation and analysis phases of even the most Agile methods. Instead they substitute what I like to call the waving of the hands form of requirements where everyone simply talks about what is needed, very often in "I'll recognize it when I see it" kind of terms. The design team does their best to interpret these statements, goes away and comes back with something that can be critiqued. The progressive elaboration of models and prototypes will allow an experienced team to eventually drive to a solution.

So what is wrong with this approach? After all, it does produce a solution. Is it optimal? Who knows? Is there any traceability to the design decisions made? Probably not. Does this sound like engineering? Emphatically no. We can do better.

What this approach lacks is the top-sight and planning that enable an architecture centric approach. Many solutions do not depend upon an architecture centric approach to achieve business success. When the solution is self-contained, highly derivative of a prior effort or does not have exceptional quality requirements, the emergent properties of the system will probably not be difficult to achieve when there is little or no "big analysis up front." But this is not the forefront of software engineering today and the solution to these challenges has not yet been found.

Emergent properties of a software system do not derive from one or even a small number of design decisions made when designing the product. Rather they emerge from a collection of many, most or sometimes all of the elements that comprise the system that have cross-cutting concerns addressed in a manner that allows the ensemble to achieve the collective goal. When the top-level decomposition of responsibilities has been properly done, these emergent properties can be achieved by independent developers working on sub-systems within the larger ensemble. But too often poor choices made in the first few design decisions can block the achievement of an emergent behavior even when all purely functional properties exist in the finished product. If the emergent properties that exist do not satisfy the business need, the product is rejected. But if the tradeoffs provide a product that "satifices", the product will be accepted and since the knowledge of what might have been is at best speculative (at worst, vindictive), the missed opportunity will never be known.

This can be improved by recognizing the key decision making role the client plays throughout the design process. The key challenge faced in trying to include the client, though, can be easily seen in a near universal scenario. The client has established a timeline and budget for the project. Then the requirements gathering begins. At some point, an astute engineer will observe that it is possible to get the needed functions and qualities a, b, and c at levels of x, y, and z and this combination is judged unacceptable. The engineer turns to the client and says, which are you willing to sacrafice. The client says "none. I want them all." What is really being said here is that the client is abrogating their responsiblity to be a decision maker in the project. If the engineer is correct that the qualities cannot all be achieved simultaneously (time and budget being two of those qualities), then the decision is foisted upon a team member to make a decision for the client. Just as the client felt cornered when asked to sign off on the requirements document, so too does the designer feel abandoned just when he needs the client the most. This is, after all, a business decision, a business decision that can have real business consequences. What is needed is for the client to engage in a form of negotiation to explore the possibilities, ensure that it really is impossible to achieve all goals simultaneously and then to take responsibility for the ultimate responsibility with the help of the business analyst, architect or whoever is in the lead design role.

So you can see that it is not as if requirements are completely elaborated at the time the project team ordinarily asks the business to sign off on them. This is an important first step and one that cannot be taken lightly. But neither can this be seen as the final word for business input. For an architecture centric approach, it must include sufficient elaboration of the qualities that can only be achieved with cross-cutting concerns that span a large portion of the code base to be developed. For any development it must at least be accurate even if it is not complete. But the impact of the aspirational goals cannot be known until the design progresses to a lower level of design and only then can the implications of that set of aspirational goals be known. As soon as possible thereafter the client must be brought back into the design process to negotiate the tradeoffs that should be made.

This process is much closer to advocacy than it is to specification. As leverage points appear there is someone to argue for the most advantageous tradeoffs that achieve their client's goals. For the client representative(s), it is to collaborate with the chief designer. For the project team, it is to do the most professional job possible in predicting the properties that will be present in the final product extended from this design.

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Tim Bender to me

show details Sep 10 (2 days ago)

In discussing a large software project with an artist, I conjured the analogy that a software product is like a painting. Each engineer is an artist with their own style and they must paint a small portion of a large masterpiece, often without ever being able to see the whole thing. Recently, I watched a movie which made me recall this analogy and I pondered it further as a way of explaining in quite a simple way some of the rather complex interactions that occur in software engineering.

The idea centers around giving groups the common task of creating the simple image of a house with a lawn, a small family, the sun, a bird, and a flower. The image would need to be simple enough to be easily reproduced by an individual, but complex enough to offer varying entry points for concept learning opportunities.

Some of these concepts are weak and need some fleshing out.
1. Requirement solicitation:
Scenario: Give a team a sheet of paper and some coloring pencils. Express to them the importance of this drawing and that it must look exactly like what is being requested. Tell them to draw "a house with a lawn, a small family, the sun, and perhaps a bird and flower or something". Being purposefully vague and leaving them to either create only the initial description, or go ask follow-up questions.
Challenge: Requesting help and/or more information.

2. Specifying interfaces:
Scenario: Give a team the exact image they are to produce and a collection of transparencies attached to construction paper (making them non-transparent). Tell the team that each person must draw something on their transparency. Inform that the transparencies will be stacked to create the complete image.
Challenge: Specifying interfaces clearly to minimize integration failures.

3. Organizing for a task:

Scenario: Give a team the exact image they are to produce and a blank canvas with some pens. Tell them that each of them must contribute something and that they will be asked to state their contribution. From there, let them self-organize.

Challenge: Skill auditing. Some members will be excellent at sketching/drawing. Some may be terrible. Those that are not gifted in this area could take on a small portion of the image or provide administrative support. A variation might include purposefully leaving out supplies that a team member must requisition.

I was curious if you would have any thoughts on this.

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Me? Have opinions? Perish the thought!

This is an interesting metaphor but I probably don't see it the same way you do.

On my visit to Vienna I had a curated tour of the Kusthistoriches (Art History) Museum. In the pre-20th century tradition of large art studios, it was common for the studio to accept commissions in very must the way you describe and in a way that does have some interesting parallels to software engineering. Each studio is headed by a master who is the creative genius that gave the studio its fame and provides the marketing effort to keep it employed. But given the output of the studio, it was not possible for the master to personally paint all the canvases. Raphael ran such a studio and we spent time talking about how to tell a Raphael from his hand versus one that he may have never touched.

In the studio system the various artists had their individual talents. The less talented might be relegated to painting landscape backgrounds, another buildings, etc. Only the most talented would paint the main subject which was always a human being. The ability to achieve life-like form and tone was prized and only the very best could capture the "essence" of a human subject. For historical paintings that had many figures, the master might paint a few of the figures but would allow the studio to fill in the remainder. This form or organization seems to be very similar to how a software project develops. There is someone with experience who is responsible for the early launch and concept. But what is different is that unless it is an architecture driven development, there is no chief designer who will oversee the design from start to finish. With each phase transition it is the project manager who oversees the progress toward the goal and not an architect. A project manager is usually more focused on the more mundane aspects of the project such as time and budget rather than the less externally visible properties of the system under development.

There is a fundamental difference between art and software. For art, the effect of the completed product is what is valued and not the qualities of the individual pieces, no matter how good. So it is with a software system. A property like security is not solely dependent upon any single component, although that cross-cutting concern will be seen in many of the modules. The lack of attention to even one point in the design can doom the security of the entire system. To one extent or another, this can be true of all the quality (non-functional) requirements placed upon the system. Performance is famously lost through a weak-link in the processing as is availability; modifiability by the inappropriate decomposition of the modules; usability by the lack of a facility for an un-do in the transactions. These qualities can be reduced to an engineering model that provides quantitative, or at least, testable properties. This is not true of art which is often said to lie in the eye of the beholder; not a good quality in an engineering project.

Ironically, I have seen many project proceed as if they were art project. The project management, the client, the business analysts, and the coders all proceed with the functional requirements only and wing it with the crap that is often offered as "non-functional requirements." This forces the team to make decisions for the client as to what qualities and what relative priorities to give to those qualities. This causes the client to not perceive the lack of some quality until they see an early prototype of the product, or worse, the finished product. Then, and only then, does the performance/availability/fault tolerance/usability/security get the attention that it deserved often with disastrous consequences to the design concepts that had guided the many hands that crafted the code.

The number 2 scenario sounds exactly like the way cell animation is done. I think the key difference here is that the transparencies are opaque and therefore block what is behind. This makes the "interface" irrelevant since there is no need for coordination between Bambi and the forest trees behind her. As long as there is no interleaving between two transparencies, there is no need for the careful coordination that is suggested with interfaces. Software, of course, is very different since most any decomposition of a function into smaller modules will create some form of interface that must be spec'd.

For any product that will be created by many hands I cannot believe that self-organization, as it is often understood, can work. I think most people take self-organization to be some form of egalitarian 'let's all get along' I do not believe this is what the Agile manifesto suggests. Rather I believe the Agile manifesto suggests that experienced and skilled professionals are more effective of organizing themselves for the task without an explicit plan from some "manager" who is not as experienced with the technology. However all the same roles will be filled. Group dynamics ensures that a leader will be selected and that the group will go through the steps of forming, storming, norming and performing. Self-organization will also do nothing to prevent the group dysfunctions that affect traditional forms of management as well.

Going back to your example, if a group of artists are given a commission and left to self-organize, the leader that emerges is not guaranteed to be the best artist. It is often true in engineering circles as well. Arrogance, self-confidence, domineering personalities are the most likely to be the group leaders. When this is also the most talented individual and has the leadership skills to bring the team along, the results can be striking. But it can just as easily lead to disaster or a mediocre product too.

Availability versus Fault Tolerant

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What is the difference between a highly fault tolerant and a highly available system?

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Edmond Lau, Quora Engineer

26 votes by Todd Lipcon, Kimberly Wang, Scott Nyce, (more)

While availability and fault tolerance are sometimes conflated to mean the same concept, the two terms actually refer to different requirements. Designing for high availability is a stricter requirement than designing for high fault tolerance.

Availability is a measure of a system's uptime -- the percentage of time that a system is actually operational and providing its intended service. Service companies, when offering service level agreements (SLAs) to their customers, usually quantify their availability in nines of availability. Carrier-grade telecommunication networks claim "five nines" of availability [1, 2], meaning that the network should be up 99.999% of time and experience no more than 5.26 minutes of downtime per year. Amazon's S3 covers three nines of availability (99.9% uptime) in its SLA [3] and offers a service credit if it is down for more than 43.2 minutes per month.

Fault tolerance refers to a system's ability to continue operating, perhaps gracefully degrading in performance when components of the system fail. RAID 1, for example, by mirroring data across multiple disks, provides fault tolerance from disk failures [4]. Running a hot MySQL slave that can be promoted to a master if the master fails, or eliminating Hadoop's NameNode as a single point of failure [5] are other examples of making a system more fault tolerant.

Making individual components more reliable and more fault tolerant are steps toward making an overall system more highly available; however, a system can be fault tolerant and not be highly available. An analytics system based on Cassandra, for example, where there are no single points of failure might be considered fault tolerant, but if application-level data migrations, software upgrades, or configuration changes take an hour or more of downtime to complete, then the system is not highly available.

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[1] http://en.wikipedia.org/wiki/Car...
[2] http://www.windriver.com/announc...
[3] http://aws.amazon.com/s3-sla/
[4] http://en.wikipedia.org/wiki/RAID
[5] http://www.cloudera.com/blog/201...Suggest Edits

What is a Software Product?

I have just completed another seminar at SEI and I want to return to the subject of the prior post. However I am going to recast it into an answer to the question "What is a software product?"

I think most people are likely to take the question to refer to a consumer product like Word or Windows 7. In this case, the product primarily consists of an executable module but no source code. In addition, to make it fit for its intended use, there are several other assumed artifacts associated or imbedded into the product. One is either an installer application or instructions on how the product is to be placed into the intended environment. In addition, there is an implied deliverable which will instruct the end-user how to perform the tasks for which the product intended using the product. These days that is often left implied more than explicit as many products are designed to be self-evident. This means that the intended end-user has sufficient experience with similar user interfaces that the use can be learned with some exploration and no explicit training. Of course this is not always the case and products may either embed the user manual into the product or provide it as a separate artifact.

There is another sense of software product though. If you consider the automobile factory that turns out cars, the cars are products to be sold to consumers. However the factory itself is an asset that can be sold to another auto maker and retooled for their use. In a similar way, source code is a major component in a product that allows a software vendor to create software products. This "software factory" is a tangible asset and is recognized as that through intellectual property laws and common sense. (To avoid some awkward language, from here on, when I refer to a software product, I am using this second sense of the term and will ignore products that only include executables. )But is the source code the entire asset? If we were to sell our intellectual property to another, what can reasonably be considered part of the asset?

In the rush to market, many software vendors are willing to sacrifice the quality of the allied artifacts of the complete system. While this helps to achieve the end goal of creating a working system, it creates technical debt in the deferred maintenance on the artifact with a measurable increase in cost to the total cost of ownership. If the product will never be modified, the complete lack of supporting documentation for the product is reasonable. Even if some was produced during the initial construction of the product, there is no reason to keep it since it will never be read. But how many software products are created that are never intended to be modified? The correction of latent defects, changes in the environment, new requirements, are just a few of the many reasons why the maintenance phase of a software product life cycle is typically the costliest. To ignore the needs of this phase of the product life-cycle are foolish and self-defeating. Therefore any technical debt incurred from the initial development will eventually need to be paid if the consequences of that debt are to be avoided.

The platonic ideal that is sought is some form of self-documenting code. While local comments, when done well, or even well written code without comments, can often be understood without additional commentary, large software systems cannot be self-documenting since many issues transcend individual modules. A software engineer may be able to reproduce the information needed from the source code alone, or at least find a way to insert the modification without it, but this is most likely a more expensive fix than it would have been had the recreation work not been needed. The lack of adequate support for the code base increases maintenance cost. Further, until a code base automatically includes self-documenting ways to explain design choices that transcend individual module, this kind of documentation will continue to exist outside of the source code itself.

This highlights a weakness in the current practice of software engineering management. The true value of this artifact is discounted by management. Since the increased support cost can never be quantified, there is no self-correction of management attitudes. The continued ratio of maintenance cost to total life-cycle cost will remain the same. Worse, there are two compounding effects from this. First, the best information about the design of the system often only exists in the minds of the developers. When they leave the project, it is usually lost for good. Even if they remain in the same organization, the fidelity of the information is lost over time. Second, without an adequate understanding of the design principles used in constructing the product, a maintainer is likely to undermine some of the design clarity that requires restraint on the part of the coder due to ignorance. It is as if the architect leaves no plans for a building behind and the maintenance engineer tries to knock out a wall only to discover an unexpected support post or beam. Even worse would be to not recognize the structural nature of the element during the remodeling and remove it, thus weakening the structure increasing the risk of structural failure.

As Agile methods gain wider use in industry, some inexperienced developers are likely to believe that producing good design documentation is just a bother. A lack of professional development, the desire to just get on with their career, an ignorance of how to best document the design, or some combination of all three likely contributes to the poor quality of this product artifact. Often professionals do not even consider the design artifact to be part of the product itself but view it as some form of construction artifact that serves no purpose after delivery. Certainly many management teams do not appreciate, nor know how to evaluate, the quality of these allied artifacts.

The lack of attention given to the maintenance phase infrastructure and staff needs is a significant blind spot. It has always been a function that has suffered from lower status than the initial construction. As the product life cycles of these software products has gotten longer, there is likely to be at least some far sighted management teams who will eventually realize that long-term profits can be improved through a reduced maintenance phase in their software assets. Once that begins to happen, the types of design documents that most efficiently support the maintenance needs will become the object of study. Until then, these support staffs will continue to be expected to do their jobs with less than ideal knowledge transfer and the need to continually read the minds of developers who are no longer around to ask.

Program Documentation and Software Architecture

A friend wrote me about the frustration of performing software maintenance in an environment largely devoid of good program documentation. He finds that he must spend a great deal of time just trying to understand how the various classes relate to each other before he can begin to focus on finding the source of a bug or trying to decide how to add a piece of functionality. I feel for him. I have been there and I suspect most programmers at some point in there career have as well. It is an interesting way to peel back some truths about the software development life cycle.

The first truth is that modern languages do a poor job of capturing the larger abstractions of their design in a way that is self-maintaining. It is possible to create a code base that has good supporting documentation of the design underlying the code. However this documentation is separate from the code. Without proper management discipline, the supporting documentation will deviate from the as-built system, if it ever matched in the first place. At the higher levels of abstraction in the design, this is exactly what is described as the system architecture.

What a maintenance programmer wants in the software system is the quality of maintainability. This is greatly enhanced by the presence of good supporting design documentation. One of the key attributes desired in this documentation is the tracability of a requirement to the specification to the code which implements that quality. When the only artifact available is the source code, this is rarely possible since the relationship is never one-to-one and usually not even many to one. Instead it is a many to many relationship between requirement and code. The consequence of this is unintended consequence and it has cost many programmers sleepless nights that they search for ways to undo the unintended consequence of their fix or enhancement. With current, accurate and complete documentation, the maintenance programmer has a far greater chance of more quickly understanding how the code implements the function (or non-functional quality) and making informed decisions about how best to make the change or fix the bug consistent with the original design and without introducing a new bug.

The sad fact is that the majority of shops do not have even inaccurate design documentation that reflect their production systems. There are a few reasons for this but in the end it always is indicative of poor management. First, there must be management discipline to enforce the delivery of design documentation with a system. Second, the professional staff must have the skills and discipline to create usable documentation. Third, the tradition of looking upon maintenance programmers as less-than developers is short-sighted when viewed from the perspective of the entire system life-cycle.

If the development staff and maintenance staffs are part of the same organization, management has an excellent opportunity to evolve a site standard for the design documentation that will be most helpful to the maintenance organization. When they are within the same larger organization this is a straightforward management task. Peer reviews by the maintenance staff of the documentation to be turned over and the empowerment of the maintenance organization to resist turnovers that are incomplete or inaccurate will allow the maintenance organization to provide the kind of efficient and quality service that is expected of them.

If the development organization is not within the same organization, many other problems occur. Often development is out-sourced to a professional organization. While they will offer a high-value service, they will be constrained by the terms of their contract. Sadly, the needs of the maintenance and operational organization are often not given proper thought if they are even considered at all. Yet the statistics show that many systems have extended production and maintenance periods and that the money spent in those periods far exceeds what is spent in the initial development. Providing artifacts that reduce the cost and increase the efficiency of these processes is enlightened self-interest. Assuming the maintenance organization has a standard way that they document their system design, the development organization should be contracted to provide an acceptable product at delivery.

Since the beginning of system development, the emphasis has always been on the finished, working product with no regard for the artifacts that can be associated with that. Few shops even have a filing system in place to keep the products of the system development in a way that allows their review. More often than not, those products are boxed and remain in the project manager's office until he leaves the organization and are then discarded with no review.

This emphasis on the end-product alone extends to management decisions regarding what is important when a project inevitably is pressed to deliver and the schedule has slipped. Rarely will the staff be driven to deliver documentation contemporary with the product. This separation of the product and the documentation subverts the review process (if it exists) and diminishes the quality of that product. Often errors in the documentation are only caught much later when the maintenance staff must use it to perform their work.

Since the design artifacts are never directly delivered, they often depart from the as-built system. Without the professional and management commitment to create and preserve high-quality design documentation, it will not happen. This is as much due to the lack of professionalism within the management of the maintenance staff. A seasoned maintenance staff with experience will push for and receive good documentation that will support their job function.

Overspecification

One of the key concepts in software engineering is the need to avoid over specification. It is natural that at some point in the decomposition of the specification of a system to be created that the specifier resorts to a description of how to do it instead of a statement of what must be done. When you drill down into this the problem is the difference between denotational semantics versus axiomatic semantics. In the first, the problem to be decomposed is given in what is hopefully the most abstract algorithmic way possible by the specifier. The problem is that it assumes there is only one algorithm possible for the solution and it locks the implementor into that algorithm.

The alternative is the axiomatic semantics of stating the pre- and post-conditions as well as any invariants in the required solution. This at once gives the implementer the choice of algorithm and implementation choices possible in the solution set. But at the same time it gives the implementer no direction as to how it can be achieved. Traditionally in commercial work the axiomatic method of specification has not been used merely because of the difficulty of making these statements about the required implementation. They are seen in formal methods but the difficulty of implementing formal methods is well known.