Add concepts

source/release/migrate/2.0.0.md

@@ -10,19 +10,23 @@ To gather the required knowledge for migrating a language project, go through th
 
 ## Differences
 
-### Terminology
+### Concepts
 
-language specification
+Spoofax 2.0 introduces several new concepts and terminology.
 
-language component
+A *language specification* is the specification of a language using meta-languages.
 
-language implementation
+A *language specification project* specifies a *language component*. When the specification is compiled, the result is a component which can be loaded into Spoofax. A language component has specifications and implementations for parts of a language, such as its parser, pretty-printer, analysis, transformations, editor services, etc.
 
-language
+A component contributes these parts to a *language implementation*. Multiple components can contribute to the same language implementation, and components can contribute to multiple language implementations. In the most simple case, a single component contributes all parts of the language to a single implementation.
+
+Language components can *depend* on other language components to depend on parts of a language. Currently, there are two kinds of dependencies: compile and source dependencies. A *compile dependency* on a language component is used to compile source files of that language component. For example, a compile dependency on NaBL will ensure that all <span class='file'>.nab</span> files are compiled into <span class='file'>.str</span> files.
+
+A *source dependency* is used to depend on source files of a language component. Source dependencies are used to depend on libraries, for example to depend on a Stratego library for name and type analysis. They are also used compose multiple language components into a single language component, for example to do language extension.
 
-language specification project
+A *language* is the more abstract notion of a language. For example, the Java *language* has the JDK7 and JDK8 *implementations*, which each have front-end and back-end *components*.
 
-end-user project
+An *end-user project* is a project with programs of an end-user language, in contrast to a language specification project which has programs of meta-languages. For example, a Java project is a Java end-user project, whereas the JDK project is a language specification project.
 
 ### General
 
@@ -34,7 +38,7 @@ generated files
 
 #### Projects
 
-Language specification projects are no longer Eclipse plugins so that they can be used outside of the Eclipse platform as well.
+Language specification projects are no longer Eclipse plugins, so that they can be used outside of the Eclipse platform as well.
 
 ##### Importing