When you add a facet to a project, that project is configured to perform a certain task, fulfill certain requirements, or have certain characteristics. For example, the EAR facet sets up a project to function as an enterprise application by adding a deployment descriptor and setting up the project's classpath.
You can add facets to Java EE projects and other types of projects that are based on Java EE projects, such as enterprise application projects, web projects, and EJB projects. You can add facets to a Java project, by selecting the properties page of the project and selecting . Typically, a facet-enabled project has at least one facet when it is created, allowing you to add more facets if necessary. For example, a new EJB project has the EJB Module facet. You can then add other facets to this project like the EJBDoclet (XDoclet) facet. To add a facet to a project, see Adding a facet to a Java EE project.
Some facets require other facets as prerequisites. Other facets cannot be in the same project together. For example, you cannot add the Web Module facet to an EJB project because the EJB project already has the EJB Module facet. Some facets can be removed from a project and others cannot.
Facets also have version numbers. You can change the version numbers of facets as long as you stay within the requirements for the facets. To change the version number of a facet, see Changing the version of a facet.
For information about Project Facets, .settings folder and Builders, see What is new in version 7.0 (Eclipse v3.2/WTP v1.5+) J2EE Projects: Project Facets, .settings folder and Builders.