Overview

Types for digital objects consist of two components, servlets and type signatures.

Type signatures define the visible interface to a type. For instance, a book type might have a method GetPage(int pagenum) which would retrieve a page. A type signature describes a types interface, irrespective of the underlying implementation. Signatures exist as executable modules, and are dynamically loaded by the server as needed. Currently, Java class files are the only type of executable supported.

The actual implementation of the type is defined in a servlet. Just as with type signatures, servlets are dynamically loaded executables. Java is the only executable format supported at this time. Digital objects are created by connecting sets of data to the generic types defined by a type signature and servlet pair. These sets of data are called attachments.