A Keystone portal is a collection of documents of different types. The documents are typically organized in a directory structure which reflects the logical structure of the portal. The documents are represented in standard XML. A portal generally is made up from documents of different types. Each type is represented by an XML Schema that describes which data elements appear in the documents, which elements are repeatable, which are mandatory, what their types are, etc. The XML schema also contains additional information specific to Keystone, for instance whether a given element is multi-lingual, corresponds to a restricted vocabulary, etc.

The Keystone Library includes a content management system which allows editors to manage the file structure and its contents (and hence the structure and contents of the user-facing portal) via a web-based interface. Access control is supported and the system supports the delegation of responsibility for the maintenance of different parts of a portal.

The documents are generally stored as ordinary XML text files on the server's filesystem. All Keystone documents have the filename suffix .tkl. The web server is configured so that when the end-user attempts to access a document with the .tkl suffix, The Keystone Library ``user shell'' is invoked. The user shell is responsible for displaying the document to the user in a suitable way.

For the purpose of display, each document type is associated with a presentation format. In this way, a help file is displayed differently from a subject group or a metadata record, and so on. The presentation formats are realised as XSLT Stylesheets which are processed to display each type of document. So the task of the Keystone user shell is, for a given document, to determine which XSLT stylesheet should be used to display the document. Apart from the document itself, the user shell makes a range of information available to the stylesheet, such as where in the directory hierarchy the document is located, whether there are other documents nearby (eg. in subdirectories), etc. It also provides the stylesheet with functions for invoking external services such as information retrieval (searching), remote procedure calls and database access.

In summary, a Keystone portal generally consists of three basic elements:

The documents are the pivot of the system - they constitute the content of a portal. The document types are primarily used in portal maintainance. The presentation formats are used when a user views a document.

The maintenance and user-facing sides of Keystone are fully independent. You can replace the content management interface with another system, or use ad-hoc scripts or batch jobs to maintain all or parts of the contents of a site. In the same way, you can use the Keystone management interface to provide remote administration for a group of files, and then use different techniques to actually present their content to end-users (assuming you even care about presenting the content to users).