Weighting Use-Cases

Now let's consider the use-cases. The primary feature of the use-cases that we judge is their pathways. The number of pathways determines the weighting factor. The pathways consist of both the happy path and the alternate pathways through the use-case. In addition, if there are many primary exception pathways, these should also be included. If the exceptions are incidental or simple error situations, don't consider them. Remember the story I told in Chapter 4: For some applications, errors are more important than the happy path.

One area where I modify the approach used by Karner is the inclusion of includes, extends, and generalize extensions on the use-case diagram. Karner elects not to include these, but this is a concern because many of these use-cases are very robust and are much more than an alternative path (as is outlined by extends, for instance). In the text of this book, I refer to many of the include and extend use-cases as shadow use-cases. My recommendation is to include all use-cases, regardless of their type.

Another consideration is that the granularity of a use-case can be a bit subjective. Some analysts tend to create use-cases that are more coarse-grained, while others make them more fine-grained. This leveling issue can also influence the resulting weighting.

Table C-2 is the table used to apply the use-case weighting factor as input to the estimating process.

For Remulak Productions, we rate the use-cases as follows:

• Maintain Orders (12 pathways): Complex

• Process Orders (7 pathways): Average

• Maintain Relationships (4 pathways): Average

• Decision Support (11 pathways): Complex

• Invoicing (3 pathways): Simple

• Shipping (6 pathways): Average

• Maintain Inventory (6 pathways): Average

• Security (5 pathways): Average

• Architecture Infrastructure (5 pathways): Average

These factors lead us to deduce the following about Remulak Productions:

1 Simple × 5 = 5

6 Average × 10 = 60

2 Complex × 15 = 30

The result is a use-case weight of 95 (5 + 60 + 30).

Now we need to add the actor total to the use-case total to get what is called the unadjusted use-case points (UUCP). Later this number will be further adjusted according to both the technical and project team characteristics. For Remulak Productions, we get the following UUCP: