Patterns for Enterprise Applications

Avijeet Dash and Satyabrata Dash

We are going to start a new series of Design Pattern articles based on "Patterns of Enterprise Application Architecture" book by Martin Fowler et al.

Let’s refresh the definition of pattern, enterprise application and architecture before we move to content and structure of publication.

Pattern

Let’s revise the definition of pattern before we go to discuss about P of EAA. So what is a Pattern? The well-known 3-part rule inspired by Christopher Alexander to a pattern is that " A pattern is a solution to a problem in context".

Problem: We need to contain global warming.

Context: The ozone layer is depleting.

Solution: Implement stringent emission laws.

But Vlissides in Pattern Hatching insists that a pattern also must have:

Recurrence, solution should be applicable in different variation of context.

Teaching, which tells about description and resolution of forces, and the consequences of application.

Name, by which a pattern can be referred to.

Enterprise Application

Enterprise applications are normally characterized with the following similarities:

Transaction integrity

Distributed computing

Data persistence

Integration with other enterprise applications.

Volumes of data.

The challenges of enterprise applications cut through projects and a small subset of that is:

Scalability

Concurrent access

Security

Performance tuning

Development platform

Legacy connectivity etc.

P of EAA has listed a good number of enterprise application examples like payroll, patient records, supply chain, accounting, customer service etc.

Architecture

Booch, Rumbaugh, and Jacobson have explained in "The UML Modeling Language User Guide" that an architecture is the set of significant decisions about the organization of a software system, the selection of the structural elements and their interfaces by which the system is composed, together with their behavior as specified in the collaborations among those elements, the composition of these structural and behavioral elements into progressively larger subsystems, and the architectural style that guides this organization---these elements and their interfaces, their collaborations, and their composition.

Software architecture involves key decisions about the structure of the system and relationship between various components of system. In Pattern Oriented Software Architecture book, you can find mention of several architectural design patterns like

Layered architecture, pipes and filter and blackboard architecture.

P of EAA Series

P of EAA book is organized into two parts. The first part contains a set of narrative chapters on a number of important topics in design of enterprise applications and patterns, with detailed solutions have been recorded in the second part.

Some of the interesting topics in enterprise applications that the book covers are

Layering of enterprise applications

Structuring domain logic.

Structuring a Web User interface

Linking in-memory modules to a relational database.

Handling session states in stateless environments

Principles of distribution

We will mainly focus on the second part of the book that is patterns although we will summarize the discussion presented in the narratives section of the book. We will discuss one pattern every fortnight from P of EAA book. We will present the pattern in the format specified in Structure section and we will also try to provide as many examples as we can in Java and C# language.

more....

Structure

We have included a new sub-section called Anti Pattern where we will discuss the scenarios when the pattern can become an anti-pattern.The design pattern structure that we will follow is given below.

Pattern Name

Name of the pattern.

Intent

The intent will explain the context of the pattern.

In 30 Seconds

There is a business-management rule, which says if you can explain a solution in 30 seconds then you know what you are talking about. So this section will help capturing the necessity of the pattern as briefly as possible.

Motivation

Highlight the key benefits of using the pattern.

Structure

The structure will define the collaboration between various objects through an UML diagram.

Sample Code

Sample example in Java or C#.

Complexities simplified

Explain the variations of the pattern and simplify any intricacies involved in the pattern.

more....

Related Patterns

Examples of frameworks using the pattern and related patterns.

Anti Patterns

Possible scenarios when the pattern becomes an anti-pattern.

Conclusion

We introduced to P of EAA series this time and also outlined the structure that we will be following for our subsequent pattern discussions. We will discuss about Layering and Organizing Domain Logic narratives next time.

Reader feedback is utmost important to us. This is a forum to discuss about P of EAA design patterns and share practical experiences with each other. So if you have opinion or suggestion about the upcoming articles, then write us and we will incorporate them into our publications.

References

Software Design Patterns

Patterns of Software Enterprise Architecture by Martin Fowler , David Rice , Matthew Foemmel , Edward Hieatt , Robert Mee , Randy Stafford

Design Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (The Gang of Four).

Pattern-Oriented Software Architecture A System of Patterns by F. Buschmann, R. Meunier, H. Rohnert, P.Sommerlad, M. Stal

Software architecture definitions

Anti Patterns

Pattern Hatching by John Vlissides

About Authors

Avijeet Dash and Satyabrata Dash can be reached at avijeetd@yahoo.com and satyabrata_dash@yahoo.com respectively.