Chapter Summary

• Integration is the process of programmatically linking your system with others.

• Extension is the process of adding new functionality to your system through well-defined approaches, such as plug-in architectures.

• Integration and extension enable your customers to create the product they seek. As a bonus, it creates tighter customer relationships and decreases the likelihood that a customer will leave you for a competitor.

• The layered architectural pattern, which organizes various system functions in logical and physical layers, provides several excellent choices for integration and extension in enterprise-class software systems. The primary layers of a layered architecture are

  - User interface

  - Services

  - Domain model

  - Persistent data

  Sublayers may exist within these layers, and other layers may be created to handle specialized requirements.

• Whatever the structure of your architecture, build it in spikes that is, user-visible functionality driven through all layers or subsystems.

• There are several ways to provide integration and extension points at the services and domain model layers. For example,

  - Programmatic techniques, such as exposing an API

  - Registration techniques, such as creating a plug-in architecture (like a Web browser)

• Integration and extension of persistent data can be accomplished through

  - Views

  - Hook tables

  - Spreadsheet pivot tables

  - Extract, transform, and load (ETL) scripts

• The business ramifications of applications that can be extended and/or integrated include

  - A professional services organization to guide your customers in these activities

  - Training programs to ensure that your customers understand how to do this on their own

  - Certification programs to create an ecosystem associated with your application

  - A community of users around your application

  - License agreements that explicitly support integration and extension

• Any customer- facing method for integrating and/or extending your application must be carefully managed. You're making a public commitment to stability. Honor it.