Monday, February 19, 2007

Introduction to Conceptual Models and Estimation

Over on Tyner Blain, you can read Scott Sehlhorst's in-depth look at estimating the cost and duration of a software project with use case points. The method Scott describes is a functional estimation method. In this entry, I introduce an object-oriented estimation method.

Estimating the cost of a software project requires knowledge of the architecture of the product. I.e., in order to know how much time and effort it will take to develop the software, understanding the requirements is not sufficient. You have to delve into the architecture (high-level design) of the system.

Use cases describe part of the information architecture of the system. In particular, they specify the interaction design; i.e. the way users interact with the product to achieve their goals. Use cases are functional decompositions of the system. Scott's recent series of blog entries focuses on estimating with use cases.

Conceptual models are a starting point for describing the conceptual architecture of the system. Conceptual architecture is the partitioning of the system into components assignable to separate teams of developers. Conceptual models are an object-oriented decomposition of the system. As such, they expose the portions of the system that are eligible for shared use.

A desirable characteristic of a system architecture is that, to the extent possible, components of the system service multiple use cases. Conceptual models provide an architect with the first clues about how best to partition the system into components that maximize this sort of sharing. Done properly, more component sharing typically translates into substantial reductions in development time.

In my next entry, I will outline a step-by-step process based on conceptual models for estimating the cost and duration of a software project.


Scott Sehlhorst said...

Very cool, Roger. Looking forward to reading the next article. The use case points method is interesting to me, because it gives you a framework for estimating (at least ROM) before you know enough to build an estimate from a WBS.

Roger L. Cauvin said...

Thanks, Scott. Your series inspired me :-)

Functional and object-oriented estimation methods complement each other well and are great for cross-checking.