The Web supports untyped hyperlinks and does not allow modification of the artifact. Quilt  is an example of a system that supports typed hyperlinks and modifiable, hyperlinked objects. It has been designed to support collaborative writing of a document, but users are expected to serialize their access to the shared data.
A Quilt document has a tree structure consisting of a root base node and annotation nodes. It supports several types of textual/audio annotations including revisions, suggestions, public comments, and directed or private messages and allows users to add new annotation types.
Annotations are associated with attributes, which can be predefined (such as creator and creation time) or user-defined. Attributes can be used in queries requesting different views of the document.
Quilt supports several roles such as co-author and commenter, each of which defines a set of permissions. Each user takes a particular role and is given the access rights associated with the role. The set of roles users can choose from and the permissions associated with them are determined by the collaboration style chosen by them. Quilt supports a set of predefined collaboration styles and allows users to extend this set. An example of a predefined collaboration style is the shared style, which defines three roles, Reader, Commenter, and Co-Author; puts these roles in the following hierarchy: A Commenter has all the rights of a Reader, and a Co-author has all the rights of a Commenter; and associates each role with permissions such as a Co-Author can create a base document, a Commenter can attach a comment to it, and a Reader can attach a private comment to it.
Quilt logs user actions at both a primitive, system-defined level and a more abstract, user-defined level. The user-defined level is generated in response to abstract statements explicitly made by users such as ``Reorganized section 2'' and ``I am thinking about a new data analysis for this section ...'' . It supports per-user electronic ``mailboxes'' by allowing users to see annotations directed to them without directly accessing the document. Like active databases , it allows users to associate user-defined actions with certain conditions. For instance, users can ask Quilt to send them messages when their partners make ``substantial'' changes to a document or to start nagging them as the document deadline approaches. Thus, Quilt is also an example of a system that combines message- and artifact- based collaboration.