6 Design Patterns

• File System Replacement: Deployment of Elephant as file replacement
• Checkpointing Conventional Program State: How to recover the application state as recorded in a set of interdependant standard classes for purposes of undo, crash recovery and session persistence.
• Persistent System Objects: Making persistent objects a natural part of your system
• Elephant as Database: Using Elephant as a database for records and user data instead of using a SQL relational Database
• Multithreaded Web Applications: Elephant is a natural match for web applications
• Real-World Application Examples: See some real-world applications Elephant has been used for and a brief discussion of how it was used and any novel uses of Elephant.

This chapter explores different ways that Elephant can be used to solve common problems in user programs. The term “Design Pattern” may be overkill as there is no formal specification of patterns. However the goals is similar to classical design patterns: provide a coherent description of how to approach ceratain common problems using Elephant as an enabling tool.

Most of this chapter falls short of a tutorial in the application of a pattern. Instead it provides a conceptual guide to implementing the pattern along with some code examples to show how Elephant features are invoked to support the pattern.

The authors hope that users of Elephant will find this a good source of inspiration for how to apply Elephant to their own programs and that they will be motivated to contribute design patterns of their own.