Make Agents Yourself

h1. SpeADL Minus Reference

In SpeADL, a set of abstractions are provided to define traditional component-oriented architectures.

With it, it is possible to define components and compositions of components, called composites, and to implement them in Java while keeping a strong link between definition and implementation by relying on an Eclipse plugin.

A component is made of two elements: a component class definition using SpeADL and an implementation using Java.

From the SpeADL definition, an abstract Java class is automatically generated and then relied upon through the Java extension mechanism to implement it in a safe manner.

h2. Namespaces

Components and composites are defined inside namespace using the keyword *namespace*.

A namespace plays the exact same role as a package in Java.

In a SpeADL file, there can be many as namespace (as well as nested ones) as wanted.

Hence a namespace does not have to follow the name of the directory it is located in as in Java.

Here is an example of namespace declarations:

<pre>

namespace simple {

	namespace things {

	}

}

namespace simple.stuffs {

}

</pre>

Each namespace declaration can contain any component as desired as we are going to see.

h2. Imports

As in Java, it is possible to import existing types into a file to avoid referring to them with their fully qualified name (i.e., including their package or namespace) using the keyword *import*.

The syntax is similar to Java:

<pre>

import java.util.Collection

import java.util.*

import simple.stuffs.*

</pre>

Notice that namespace of components are also considered to import component class definitions, and that there is no semi-colon ";" at the end of the line.

The imports can be automatically handled and reorganised in Eclipse using the *Ctrl-Shift-O* shortcut as in the Java editor.

h2. Components and Ports

A component is made of a component class definition and an implementation: it can then be instantiated 

The definition gives it a name and a list of ports that are either provided or required by the component.

Each port has a name and an interface.

An interface is understood as a Java interface, i.e., a collection of methods.

A component that provides a port must thus provide an implementation for its interface.

Inversely, a component that requires a port can use in its implementation the methods of the interface of the required port.

A component with required ports must be composed with other components so that there exist an actual implementation of the interface of the required port: this is covered in the next section.

When implementing a component, one only has to take care of implementing the provided port, and can exploit the required ports without assuming anything about their implementation and who provides it.

This is what makes a component fundamentally different from an object.

A component is defined using the following syntax:

<pre>

import my.interfaces.*

namespace simple.stuffs {

	component MySimpleComponent {

		provides p1: AnotherJavaInterface

	}

	component MyBeautifulComponent {

		provides portName: AJavaInterface

		requires anotherPortName: AnotherJavaInterface

	}

}

</pre>

A component is defined using the keyword *component*, has a name and can contains as many port declaration as wanted.

A port has a name and an interface.

The keywords *provides* and *requires* respectfully represents ports that are provided and required by the component and are a mandatory keyword when defining a port inside a component.

Obviously, having an interface means that there must exist already an interface defined with the same name.

Such a definition is done in Java as one would normally do, for example, as follow, in Java files:

<pre>

package my.interfaces;

public interface AJavaInterface {

  public String aMethod(Integer param1);

}

</pre>

<pre>

package my.interfaces;

public interface AnotherJavaInterface {

	public Integer test();

}

</pre>

In SpeADL, one can use completion to complete interface names.

Also, the shortcut to organize imports will take interfaces into account.

h2. Implementations

To implement a component, one has to extend the abstract class generated automatically by the Eclipse plugin.

For example, for the previous example of component, a Java class *simple.stuffs.MyBeautifulComponent* was generated (in the speadl-gen folder, separated from the src folder).

It is not needed to look at the generated code to use it: when extending the class, some abstract methods must be implemented.

It is a good idea to use the errors shown by the Eclipse Java editor and their quick-fixes to quickly generate the skeleton of the implementation itself.

Each provided port *p* of interface *I* must be implemented by overriding a method called *I make_p()* which returns an implementation for the port used during the whole life of the component (i.e., the *make_p()* method is called only once to construct the port when the component is instantiated).

Usually, one returns in this method an anonymous instance of the interface as the following Java files show:

<pre>

package testpackage;

import my.interfaces.AnotherJavaInterface;

import simple.stuffs.MySimpleComponent;

public class MySimpleComponentImpl extends MySimpleComponent {

	@Override

	protected AnotherJavaInterface make_p1() {

		return new AnotherJavaInterface() {

			@Override

			public Integer test() {

				return 10;

			}

		};

	}

}

</pre>

<pre>

package testpackage;

import my.interfaces.AJavaInterface;

import simple.stuffs.MyBeautifulComponent;

public class MyComponentImpl extends MyBeautifulComponent {

	@Override

	protected AJavaInterface make_portName() {

		return new AJavaInterface() {

			@Override

			public String aMethod(Integer param1) {

				return "" + param1 + " and " + requires().anotherPortName().test();

			}

		};

	}

}

</pre>

But the same result can be obtained by implementing the port directly by the component implementation as follow:

<pre>

public class MyComponentImpl extends MyBeautifulComponent implements AJavaInterface {

	@Override

	public String aMethod(Integer param1) {

		return "" + param1 + " and " + requires().anotherPortName().test();

	}

	@Override

	protected AJavaInterface make_portName() {

		return this;

	}

}

</pre>

We can see that the class extends simple.stuffs.MyBeautifulComponent and that it overrides a method named *make_portName()* after the name of the provided port.

Finally, the *requires()* method (inherited from the extended generated class, *MyBeautifulComponent* in the example) gives access to each of the required ports (e.g.,*requires().anotherPortName()* in the example).

A port being an implementation of an interface (and not of an operation), it is then necessary to call the desired method on it (e.g., *requires().anotherPortName().test()* in the example).

Of course, nothing else is required than calling it to use it: as we are going to see now, the implementation of a required port is provided by another component composed with the requiring component.

h2. Composites

While defining a component class with a name and ports in SpeADL is only a definition of its external interfaces, a composite of many components connected together is already a partial implementation of this definition.

A composite, on top of provided and required ports, contains parts. A part is structurally similar to a class member in Java.

A part is declared using the *part* keyword and the name of the component class of the part.

Furthermore, if the component class of the part has required ports, then a part will also contain bindings for these required ports using the keyword *bind*.

An example follow:

<pre>

namespace simple.stuffs {

	component MyComplexComponent {

		provides p1: AnotherJavaInterface

		provides p2: AnotherJavaInterface = s.p1

		requires p3: AnotherJavaInterface

		part b1: MyBeautifulComponent {

			bind anotherPortName to s.p1 

		}

		part b2: MyBeautifulComponent {

			bind anotherPortName to p1

		}

		part b3: MyBeautifulComponent {

			bind anotherPortName to p3

		}

		part s: MySimpleComponent

	}

}

</pre>

The keyword *bind* is followed by the name of the required port that is to be bound (completion can be used), then by the keyword *to* then either by:

* The name of another part, a dot, then a provided port of this part (as for *b1* in the example).

* The name of a provided port of the component containing the part (as for *b2* in the example).

* The name of a required port of the component containing the part (as for *b3* in the example).

Furthermore, another type of binding is a delegation of a provided port to another port.

It is declared using the = sign after the provided port declaration (as in *p2* in the example) and can be followed either by a reference to the port of a part, a provided or a required port of the component, as with the normal bindings.

h3. Implementation of Composites

As with the implementation of non-composite component classes, a Java class is generated from the description and it must be extended in order to specify the implementation of the provided ports and of the parts.

Each part *p* of component class *C* has a corresponding abstract method *C make_p()* to override and which must return an instance of an implementation of *C*.

For example:

<pre>

public class ComplexCompImpl extends MyComplexComponent {

	@Override

	protected MySimpleComponent make_s() {

		return new MySimpleComponentImpl();

	}

	@Override

	protected AnotherJavaInterface make_p1() {

		return new AnotherJavaInterface() {

			@Override

			public Integer test() {

				return parts().s().p1().test();

			}

		};

	}

	@Override

	protected MyBeautifulComponent make_b1() {

		return new MyComponentImpl();

	}

	@Override

	protected MyBeautifulComponent make_b2() {

		return new MyComponentImpl();

	}

	@Override

	protected MyBeautifulComponent make_b3() {

		return new MyComponentImpl();

	}

}

</pre>

As we can see, the bindings and other connections inside the components are totally taken care of by the generated code and the implementation only needs what is Java-specific.

It becomes very easy to define new compositions without extra boilerplate code.

Also, it is possible to access to the provided ports of the part from within the implementation of a composite by using the method *parts()* (as in the implementation of the port *p1* in the example).

h2. Instantiation

In order to instantiate a component, one need an instance of an implementation of the component and to call the *newComponent()* method (present in the generated class) to get an instance of the component.

Only component without required port can be manually instantiated: if a component has required ports, it must be composed with other components in a composite component.

For example:

<pre>

MySimpleComponent.Component c = new MySimpleComponentImpl().newComponent();

System.out.println(c.p1().test());

</pre>

As we can see, once we have an instance of a component, we can call the methods of its provided ports.

The same applies for composite components, the instantiation of the part of a composite is done automatically by the generated code.

h2. Component Initialisation

When the implementation of a component is instantiated (before calling *newComponent()*), its constructor is of course called but the component itself is not yet initialised: in particular its provided required ports and parts can't be called at that time.

In order to do some initialisation at the instantiation of a component (during the call to *newComponent()*), one can override the *void start()* method in the implementation as follow:

<pre>

public class MySimpleComponentImpl extends MySimpleComponent {

	@Override

	protected AnotherJavaInterface make_p1() {

		return new AnotherJavaInterface() {

			@Override

			public Integer test() {

				return 10;

			}

		};

	}

	@Override

	protected void start() {

		// do some initialisation using the requires() or the parts(), create a GUI, etc...

	}

}

</pre>