You Can Reuse Without A Big Investment

When salvaging you got to be the tug that pulls what you need to the surface.

The most effective way to reuse software components is from a repository of crafted, handpicked libraries that were tailored specifically for reuse. However, this requires considerable investment in both time and money. It is possible to reuse in the short term through a technique called salvaging.

Salvaging is asking others in your organization if they have built a software component that does X. You find it, you adapt it, you employ it. This may not be efficient in the long term, but it certainly works now; and then you have no more excuses not to reuse.

To my experience, few organizations are willing to allocate time for the proper care and upkeep of a repository of reusable software components. Salvaging might be your only option. And it gets you talking to your peers on different teams. This communication is like grease that will make future interactions smoother.

Know Your Application

No matter how well the requirements have been written, the selection of optimal architectures and algorithms is very much a function of knowing the unique characteristics of an application. Expected behavior under stress situations, expected frequency of inputs, life-critical nature of response times, likelihood of new hardware, impact of weather on expected system performance, and so on are all application-specific and often demand a specific subset of possible alternative architectures and algorithms.


Reference:
Curtis, B., et al, "A Field Study of the Software Design Process for Large Systems," CACM, November 1988.

Store Requirements in a Database

Keep in mind that the follow quote is from 1995. It is still completely relevant.

Requirements are complex and highly volatile. For these reasons, storing them in electronic media, preferably a database, is a good idea. This will facilitate making changes, finding implications of changes, recording attributes of specific requirements, and so on.
      Some of the things you want to store in the database are unique identifier (Separately Number Every Requirement), the text of the requirement, its relationship to other requirements (such as more abstract or more detailed descriptions of the requirement), importance (Prioritize Requirements), expected volatility, pointers to its sources (Record Why Requirements Were Included), applicable product versions (Identify Subsets and Give Every Intermediate Product a Name and Version*), and so on. Ideally, the requirements specification itself is nothing but an organized "dump" of the entire database.

I have used JIRA. There are many tools like it. They can do all of the above, but it is up to the person creating a ticket in JIRA to ensure those things are done. I think they are really important so I'm going to list them again.

• Create the ticket in a backlog or project that is unique. Do not lump unrelated tickets together. This will result in a "fatlog" - a fat backlog that is difficult to groom and manage.
• The text of the requirement goes in the "description". The "summary" is not where the requirement should be detailed. Personally, I think systems like JIRA should not allow tickets that have no description to be saved. Engineers should refuse to estimate such tickets and Product Owners who create them should be ashamed.
• JIRA has a feature to link tickets. Use it. If there is a dependency then utilize the sub-task feature. Make a story that encapsulates both tickets and make them linked sub-tasks. Use the system to track if everything for that requirement is actually done.
• Order the tickets by importance. There can only be one highest priority and it at the top.
• Use comments to document the sources/stakeholders for a ticket. Do not use comments to have a discussion about a ticket. Email, call, instance message, etc with the people involved. If you absolutely must use the comments section of a ticket to have a discussion then clean it up later. Delete anything that will mislead people reading the ticket. If you want to save the history then move that stuff into a document and attach it to the ticket with a title that makes it clear that it is for history and it is not the requirement. The actual requirement is in the description.
• Ensure that you put what product the ticket applies to either in the summary or the description. You might be inclined to think that it is clear by where the ticket sits. For example, the ticket is in the product A backlog. Invariability, someone is going to get confused and try to work that ticket for product C which is really similar to product A. I've also seen people accidentally move a ticket to a different backlog then not be able to figure out where it belonged.
• If you can't take the issues in a JIRA backlog and print them out in order and call that your software requirements specification (SRS) then your backlog is a mess and you have some work todo.

6 Tips to Make Your Backlog Lean

Self-Destruct TBDs

A software requirements specification (SRS) with a TODO or TBD (To Be Determined) note is obviously not complete. There may be good reasons for approving and starting work on a project with a TBDs in the specification. This is particularly true for requirements whose precision are not critical to fundamental design decisions.

When you create a TBD, be sure to footnote it with a "self-destruction note," that is, specify who will resolve the TBD and by when.


Reference:
IEEE, ANSI/IEEE Guide to Software Requirements Specifications, IEEE Computer Society Press, Washington, DC, 1994.

Specify When Environment Violates "Acceptable" Behavior

Requirements specifications often define characteristics of the system's environment. This information is used in making intelligent design decisions. It also often implies that the developer is contractually obligated to accommodate such characteristics. What happens after deployment when the environment exceeds the specified limits?

Suppose the requirements for an air traffic controller system specify that the system shall handle up to 100 aircraft in a sector simultaneously. They system is built and correctly satisfies this requirement. Three years later 101 aircraft accidentally enter a sector. What should the software do? The possibilities are:

1. Print an error message.
2. Crash.
3. Ignore the 101st aircraft.
4. Process all 101 aircraft but perhaps not satisfy some other timing constraint (such as how often the screen is updated).

Obviously, options 1, 2, and 3 are unacceptable. Yet they are valid system responses as (not) stated in the requirements. The right solution is to explicitly state in the software requirements specification (SRS) the expected system response when the environment exceeds any of the constraints defined for it.


Reference:
Davis, A., Software Requirements: Objects, Functions, and States, Prentice Hall, Englewood Cliffs, 1993.

Specify Reliability Specifically

Software reliability is difficult to specify. Don't make the problem even more difficult by being vague. For example, "The system shall be 99.999% reliable" means nothing.

Does it mean that the system cannot be "down" more often than 5 minutes every year but that it is okay to occasionally make a mistake (for example, a hotel reservation service may occasionally mix up hotel details). Or does it mean that it must make no more than one mistake every 100,000 transactions (for instance, a patient monitoring system cannot cause the death of more than one out of every 100,000 patients)?

When writing requirements, differentiate between:

1. Failure on demand.
•  What is the likelihood, measured as a percentage of requests, that the system will fail to respond correctly? For example, "The system shall correctly display 99.999% of hotel information."
  
2. Rate of failure.
•  This is the same as "failure on demand" but it is measured as a percentage of time. For example, "The system may fail to report hotel information correctly no more than twice a year."
3. Availability.
•  What percentage of time may the system be unavailable for use? For example, "The hotel reservation system shall be available 99.99% of the time in any given calendar year."

Reference:
Sommerville, I., "Software Engineering," Addison-Wesley, Reading, MA, 1992.

Write Natural Language Before a More Formal Model

Augment, Never Replace, Natural Language says to create requirements specifications that contain both natural language and formal models. Let's go a step further: Always create the natural language version of a requirements specification first. If you write the formal model first, the tendency will be to write the natural language that describes the model instead of the desired system. This also applies to writing test cases. Write the test cases first to avoid the tendency to only test the code that was written or the way it is applied.

The best approach is to (1) write the natural language, (2) write the formal model, and (3) adapt the natural language to reduce ambiguities that become apparent when writing the formal model.

Augment, Never Replace, Natural Language

"In an effort to reduce ambiguity in requirements, software developers often decide to use a notation that is more precise than natural language. This is, of course, commendable in that ambiguity is reduced (Reduce Ambiguity in Requirements) by using finite state machines, predicate logic, Petri nets, statecharts, and the like. However, in such an effort, the specification is rendered less understandable by others (Keep the Requirements Specification Readable*) who may have less computer science or mathematical background than the requirements writer.

To alleviate this problem when using a formal notation, retain the natural language specification. In fact, one good idea is to keep the natural language and more formal specification side-by-side on opposing pages. Do a manual check between the two to verify conformity. The results will be that all readers can understand something and that some nonmathematical readers may learn something useful."


Reference:
Meyer, B., "On Formalism in Specifications," IEEE Software, January 1985.

Reduce Ambiguity in Requirements

Software requirements specifications are often written in a natural language. To reduce the ambiguity of natural language apply the following techniques:

1. Performing Fagan-type inspections on the Software Requirements Specification (SRS).
2. Constructing formal models of the requirements and rewriting the natural language as problems are found (Know Formal Methods).

Reference:
Davis, A., "Software Requirements: Objects, Functions, and States," Prentice Hall, Englewood Cliffs, 1993.

Separately Number Every Requirement

"It is essential that every requirement in the requirements specification be easily referenceable. This is necessary to enable later tracing to the requirements from the design (Trace Design to Requirements) and from test (Trace Tests to Requirements)."

I recently completed a project where there was not requirements specification document. The requirements were captured in a JIRA project. For anyone using a similar system for requirements tracking, the equivalent principle would be to make a ticket for every requirement. Don't get lazy and lump several requirements into one ticket just because they are related. If they are separate requirements then they need to be tracked as separate tickets.


Reference:
Gilb, T., "Principles of Software Engineering Management," Addison-Wesley, Reading, Mass, 1988.