Texo/Design Concepts

Introduction

This page gives an overview of the main design ideas which are the basis for the Texo project.

Runtime Model

Texo differs from other code generation approaches outside of EMF in that specific attention is paid to support of a runtime representation of the domain model. The domain model is expressed in ecore or XSD and with the model annotations drives the code generation. At runtime it is critical to also have the possibility to work with the domain model and to access the generated code using model constructs.

Model-driven functionality (at runtime)

Many applications have one or more functions which really make sense to implement at model level instead of at specific instance/type level. A runtime model is makes it very easy to implement functions at runtime such as:

• archiving: implement a generic archiving model which uses the runtime model to interrogate objects and retrieve changed and new property values.
• security: it makes sense to define security also using entities from the domain model. To support security definition changes at runtime it must be possible to address the model at runtime. To check security at runtime one needs access to the runtime model also.
• export/import: export and import functions in an application can benefit from generic model-based logic. Implementing export/import using the runtime model is very efficient compared to writing a specific export/import per type in a system.

Another usage scenario for having the model available at runtime is that the model elements can be used to define other system components. An example of this is a system which allows users/consultants to define the user interface themselves through a user interface. To support the user/consultant in defining a user interface he/she must be able to select elements from the runtime model to define fields in a form or columns in a grid.

Runtime Model in Texo

The Texo runtime model is an ecore model. The ecore model can be reached through the generated ModelPackage class of a

Work with generated code

There are roughly two schools of thought regarding how to handle and work with generated code.

One school of thought states that generated code should never be changed manually. Generated code should not be committed to a CVS. It should be possible to remove all the generated code, regenerate and then have the same situation as before. In this approach any manual/custom logic should be implemented in subclasses of the generated code. These subclasses can also be generated. This school of thought is what is propagated by developers from the [1] project.

The other school of thought states that it should be possible to change generated code. manual changes in the code should remain even if the code is re-generated. Generated code should be checked in to a CVS. This approach is followed by the [2] project.

Both groups consist of experienced, very knowledgeable developers, architects and experts on the field of model-to-text transformation and code generation.

Texo follows the EMF approach (the second school of though) because:

• it feels more natural to change/add behavior to the generated class than to a subclass.
• manual code can easily be identified inside of generated classes.
• the code generation does not update the file on the file system if it has not changed by code generation. This results in minimal changesets in a CVS, and much better, if something changes it is directly visible in CVS diffs etc.
• by checking in the generated code to cvs it is much easier for others to work with the development project as no generation step is needed after getting the project or updates from a CVS. The same applies to re-distribution of regenerated code, by checking in the generated code (and the changes) it is much clearer what has changed and when people update from the CVS they will receive a consistent state directly.
• Texo will re-organize imports and remove files which related to model elements which have been removed. As the code is checked in these removal actions are tracked in a CVS.