What makes a good spec? [closed]

Question

One of the items in the Joel Test is that a project/company should have a specification.

I'm wondering what makes a spec good. Some companies will write volumes of useless specification that no one ever reads, others will not write anything down because "no one will read any of it anyway". So, what do you put into your spec? What is the good balance between the two extremes? Is there something particularly important that really, really (!) should always be recorded in a specification?

Answer 1

The best spec is one that:

1. Exists
2. Describes WHAT, not HOW (no solutions)
3. Can be interpreted in as few ways as possible
4. Is widely-distributed
5. Is agreed-upon as being THE spec by all parties involved
6. Is concise
7. Is consistent
8. Is updated regularly as requirements change
9. Describes as much of the problem as is possible and practical
10. Is testable

Answer 2

What to put in a spec

You need to look at the audience of the spec and work out what they need to know. Is it just a document between you and a business sponsor? In this case it can probably be fairly lightweight. If it's a functional spec for a 100+ man-year J2EE project it will probably need a bit more detail.

The audience

The key question is: who is going to read the spec - A spec will have several potential sets of stakeholders:

• The business owner who is signing off the system.

• The developer who is building the system (which may or may not be you)

• QA people who have to write test plans for it.

• Maintenance staff wanting to understand the system

• Developers or analysts on other projects who may want to integrate other systems into it.

Requirements of typical key stakeholders:

• The business owner needs to have a clear idea of what the system workflows and business rules are so they can have a fighting chance of understanding what they have agreed to. If they are the only major audience of the spec, concentrate on the user interface, screen-screen workflow and business and data validation rules.

• Developers need a data model, data validation rules, some or all of the user interface design and enough description of the expected system behaviour so they know what to build. If you are writing for developers concentrate on the user interface, mapping to data model and rules in the user interface. This should be more detailed than if you are doing the development yourself because you are acting as an intermediary in a communication between two third parties.

  If you are specifying an interface between two systems, this has to be very precise.

• QA staff need enough information to work out how to test and validate the logic, validation and expected user interface behaviour of the application. A spec intended for developers and QA staff needs to be fairly unambiguous.

• Maintenance staff need much the same information as developers plus a system roadmap document describing the architecture.

• Integrators need a data model and clear definitions of any interfaces.

Key components of a spec:

I'm assuming that one is writing specs for business apps, so the content below is geared to this. Specs for other types of systems will have different emphasis. In my experience the key elements of a functional spec are:

• User Interface: screen mockups and a description of the interaction behaviour of the system and workflow between screens.

• Data Model: Definition of the data items and mapping to the user interface. User interface mappings are normally done in the bits of the spec describing the user interface.

• Data Validation and Business Rules: What checks for correctness need to be be made on the data and what computations are being made, along with definitions. Examples can be quite useful here.

• Definitions of interfaces: If you have interfaces exposed that other systems can use, you need to specify those pretty tightly. The simpler internet RFC's give quite good examples of protocol designs and are quire a good start for examples of interface documents. Clearly defining interfaces isn't easy but almost certainly save you grief down the track.

• Glue: this is where use cases, workflow diagrams and other requirements related artifacts help. Generally an exhaustive listing of these is pointless, but there will be key areas within the system where this type of documentation helps to put items in context. My experience is that selective inclusion of use cases and other requirements level descriptions does a lot to add clarity and meaning to a spec but writing up a user story for every single interaction with the system is a waste of time.

Joel (of 'on software' fame) wrote a good series of articles on this called Painless Functional Specification which I've referred people to on quite a few occasions. It's quite a good set of articles and well worth a read. In my opinion, your objective is to clearly explain what the system is supposed to do in a way that minimises ambiguity. It's quite useful to think of the spec as a reference document - what might the various stakeholders want to be able to easily look up.

Having written a glib set of bullet points about specs, the clear communication part is harder than it looks. Specs are actually non-trivial technical documents and are quite a test of one's technical writing and editorial skills. You are actually in the business of writing document that describes what someone is supposed to build. Doing good specs is a bit of an art.

The pay-off for doing specs is that no-one else wants to do them. As you've written what is probably the only document of any importance for the system, you get to call the shots. Anyone else with an agenda has to either lobby you to change the spec or somehow impose a competing spec on the project. This is a good example of the pen being mightier than the sword.

EDIT: It has been my experience that debate about the distinction between 'how' and 'what' tends to be pretty self-serving. On any non-trivial project the data model and user interface will have multiple stakeholders, not all of whom are the system's developers. Working in data warehousing will give one a taste for the chaos that ensues when an application data model is allowed to become a free-for all, and PFS should give one a feel for the potential set of stakeholders a spec has to cater to.

The fact that someone owns a data model or user interface design doesn't mean that these are just decided by fiat - there can be a discourse and negotiation process. However, as a project gets larger the value of ownership and consistency in these gets greater. It's been my observation in the past that the best way to appreciate the value of a good analyst is to see the damage done by a bad one.

Answer 3

In my experience a spec will have more chance of being read if it has the following:

• Use diagrams where possible - pictures are worth 1000 words
• Have a title page that clearly indicates what the spec is describing
• Have a style that is used throughout the document. Make all headers the same font, size and style. Make the font the same all the way through, use the same bullet styles etc
• DONT WAFFLE - Be clear concise and to the point, and don't add extra cruft to pad out your document. If a point can't be explained in a few lines of text, then maybe you need to break it down further

I have seen in companies where the person writing the spec doesn't understand the system. It's almost a way of learning the system by writing the spec. This usually ends in tears...