# How to extend ShapeChange

This page describes how you can extend ShapeChange.

The main extension points are:

- Creating a new model implementation - In case that you have another model source that is not supported by ShapeChange yet. The model could be stored in a specific file format, or be accessible through a specific server interface.

- Creating a new model transformation - In case you would like to develop a new model transformation.

- Creating a new ShapeChange target - This will allow you to derive new representations from an application schema.

How to use each of the three extension points is described in more detail in the following sections.

When developing an extension for ShapeChange, the goal should be that you do not need to modify the code of ShapeChange itself. However, if changes to ShapeChange are needed, you can fork the ShapeChange GitHub repository, modify the code as needed, and create a PullRequest once you are satisfied with the results (and all UnitTests pass).

This page also describes how you can set up your development environment.

Note | If you experience any issue with extending ShapeChange, please report it via our issue tracker on GitHub.

## 1. Creating a new model implementation

To load a model from a custom source, you need to provide a model implementation. You need to implement the following interfaces in package de.interactive_instruments.ShapeChange.Model:

- AssociationInfo

- ClassInfo

- Model

- OperationInfo

- PackageInfo

- PropertyInfo

For each of these interfaces, the package provides a class with suffix "Impl" (e.g. ClassInfoImpl), which you should base your implementation on, since these classes provide implementations for a number of the methods defined by the interfaces.

ShapeChange provides a model implementation to read a UML model from an Enterprise Architect repository. This is a good example for a model implementation. See package de.interactive_instruments.ShapeChange.Model.EA.

To instruct ShapeChange to use your model implementation, provide the fully qualified class name of your ModelInfo implementation as value of the input parameter 'inputModelType', or similar configuration parameters like 'referenceModelType'.

## 2. Creating a new model transformation

In ShapeChange, a transformation modifies a given model, with the goal to bring it in a form that is suited to derive a desired representation via a ShapeChange target. The Flattener transformation, for example, provides a number of transformation rules to simplify complex model structures, which is needed for a number of implementation environments (e.g. databases). The reusability of the Flattener to support various use cases is a key benefit of that transformation. Ideally, a new transformation is implemented in such a way that it can usefully be applied to a number of different application schemas.

Creating a new transformation requires implementing interface de.interactive_instruments.ShapeChange.Transformation.Transformer.

The execution of a transformation often requires information from the user, which can be provided via the ShapeChange configuration. More specifically, a transformation can have parameters, rules, map entries, and also a custom (XML based) configuration. The transformations that are already supported by ShapeChange provide ample implementation and configuration examples.

## 3. Creating a new target

A ShapeChange target reads a model (that has been loaded and - optionally - transformed by ShapeChange) and derives one or more artifacts from the model. These artifacts are sometimes also called implementation schemas.

Creating a new target requires implementing interface de.interactive_instruments.ShapeChange.Target.Target. Depending on the use case, a new target may also be implemented as a de.interactive_instruments.ShapeChange.Target.SingleTarget and may also implement the interface de.interactive_instruments.ShapeChange.Target.DeferrableOutputWriter. A SingleTarget processes all application schemas in the model that were selected for processing before it writes the results, while a Target does so once all the classes of a given application schema have been processed. SingleTargets should be used when the implementation needs to have information on all application schemas before the output can be created. An example of such a target is the FeatureCatalogue target, which can create a single document with information on all relevant application schemas. For further details on these interfaces, please consult their java documentation.

Just like for transformations, the execution of a target often requires information from the user, which can be provided via the ShapeChange configuration. More specifically, a target can have parameters, rules, and map entries. The targets that are already supported by ShapeChange provide a number of implementation and configuration examples.

Note | Targets often implement a number of conversion rules. Furthermore, standard encoding rules may exist that aggregate a specific set of conversion rules. Targets (like the XmlSchema target) may also define specific requirements, identified by a unique string. The de.interactive_instruments.ShapeChange.Model.Info.matches(String) method is used in ShapeChange to determine if a given model element matches one of these rules. Consequently, ShapeChange needs to know them (i.e., the rules). The rules can be registered as follows: Since ShapeChange v2.9.0: By the Target implementation, via method registerRulesAndRequirements(RuleRegistry). For further details, see the javadoc of that method. ShapeChange automatically calls the method for each Target implementation found on the classpath. Before ShapeChange v2.9.0: Target rules had to be configured in the ShapeChange code of de.interactive_instruments.ShapeChange.Options.addStandardRules(). In other words, an update of the ShapeChange code was needed.

## 4. Setting up your development environment

We describe two different setups for developing a ShapeChange extension:

- An extension that shall be incorporated in ShapeChange itself.

- An extension that shall be developed and hosted in a separate project, and just include ShapeChange as one of - potentially many - dependencies.

### 4.1. Extending the ShapeChange core code basis

To extend ShapeChange itself, and thus feed new/modified code back to ShapeChange:

- Fork the ShapeChange GitHub repository

- Clone that fork so that you have the files on your machine.

- Integrate the ShapeChange project in your IDE.

  - In Eclipse, this can be done by simply importing the project as a maven project.

- Add/modify code as necessary.

- Once you are satisfied with the results (and all UnitTests pass), create a PullRequest.

### 4.2. Developing and hosting an extension in a separate project

You can develop your ShapeChange extension in a separate project. Your model implementations, transformations, and targets would then be deployed in a separate jar, alongside the jar that contains the code of the ShapeChange core project.

To reference - and include - the jar with the ShapeChange code in your project, add the following maven dependency (with updated version number, depending on which release of ShapeChange you’d like to base your developments on; in general we recommend to keep your code in synch with the latest release):

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      <dependency>
     <groupId>net.shapechange</groupId>
     <artifactId>ShapeChange</artifactId>
     <version>2.3.0</version>
     </dependency>

The maven configuration entry to identify the ShapeChange maven repository is:

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      <repository>
     <id>ShapeChange</id>
     <name>ShapeChange repository</name>
     <url>https://shapechange.net/resources/dist/</url>
     </repository>

The AAATools project provides an example of a separate project that depends on the ShapeChange core project and implements additional ShapeChange targets.