Figure 1 is hands down my favorite one of all time.  I've been working on it for several years, evolving it through my books such as Building Object Applications That Work, Process Patterns, and the second and third editions of The Object Primer.  The boxes represent potential development artifacts, a matrix describing the relationships between the models is available as is a list linking to descriptions, and the lines represent good options when you are applying the practice Iterate to Another Artifact.

Figure 1. Strategies for iterating to another artifact.

Interesting implications of the diagram: You have multiple models to choose from. There is no starting point. Development is serial in the large.  You can see this in the fact that the left side of the diagram are mostly requirements artifacts, that as you proceed towards the right that the artifacts focus on analysis, then design, then finally code. Development is iterative in the small.  On any given day I am likely to work on several artifacts and will iterate back and forth between them. The UML doesn't provide a complete picture, instead you need to take a more realistic look at it. No one model or artifact "drives" another.  A common myth is that your data schema should drive your object schema (and vice versa).  Instead you need to be prepared to take different strategies depending on your situation. This diagram is arguably a high-level meta model relating development artifacts that implies traceability strategies for your team. What I'm really talking about is "modeling normalization" -- using each artifact for what it is good for and referring to information in other models (e.g. a use case refers to a business rule) but not copying that information. This approach ensures highly cohesive models that are loosely coupled to one another.

Figure 2, taken from the article Development Phases Examined, shows the various categories of models and how you iterate back and forth between them as needed.  It's basically an update, and generalization, of Figure 1.

Figure 2. Categories of models.

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Recommended Resources

The Object Primer 3rd Edition: Agile Model Driven Development with UML 2 is an important reference book for agile modelers, describing how to develop 35 types of agile models including all 13 UML 2 diagrams.  Furthermore, this book describes the techniques of the Full Lifecycle Object Oriented Testing (FLOOT) methodology to give you the fundamental testing skills which you require to succeed at agile software development.  The book also shows how to move from your agile models to source code (Java examples are provided) as well as how to succeed at implementation techniques such as refactoring and test-driven development (TDD).  The Object Primer also includes a chapter overviewing the critical database development techniques (database refactoring, object/relational mapping, legacy analysis, and database access coding) from my award-winning Agile Database Techniques book. Agile Modeling: Effective Practices for Extreme Programming and the Unified Process is the seminal book describing how agile software developers approach modeling and documentation.  It describes principles and practices which you can tailor into your existing software process, such as XP, the Rational Unified Process (RUP), or the Agile Unified Process (AUP), to streamline your modeling and documentation efforts.  Modeling and documentation are important aspects of any software project, including agile projects, and this book describes in detail how to elicit requirements, architect, and then design your system in an agile manner. The Elements of UML 2.0 Style describes a collection of standards, conventions, and guidelines for creating effective UML diagrams. They are based on sound, proven software engineering principles that lead to diagrams that are easier to understand and work with.  These conventions exist as a collection of simple, concise guidelines that if applied consistently, represent an important first step in increasing your productivity as a modeler.  This book is oriented towards intermediate to advanced UML modelers, although there are numerous examples throughout the book it would not be a good way to learn the UML (instead, consider The Object Primer).  The book is a brief 188 pages long and is conveniently pocket-sized so it's easy to carry around.

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