1.2.2 Link Management
Hyperwave Information Server does not store link information directly within
the source document, as is the case with most classic hypertext systems. In
these cases, because the link information is only available in the source
document, it is difficult to maintain the link consistency of (large) Web
sites. When you want to delete a document and need to know what other documents
refer to this document, you have to search through all other documents for
hyperlinks to this document. Obviously, this is prohibitively expensive for an
intranet site with tens of thousands of documents.
LINKS SEPARATED FROM DOCUMENTS
To avoid these problems with link consistency, Hyperwave Information Server has
a very different approach to link maintenance: hyperlinks are separated from
documents and stored as objects in their own right, in the same object
repository as documents, collections, etc. In the case of HTML pages, for
example, this means that the hyperlink information is extracted when the HTML
page is inserted, stored in the repository, and dynamically merged back into
the document when it is served to the user.
Links are realized as one or two objects: a source anchor defines the
region the link is emanating from (e.g., a sequence of characters in a text or
a region of an image). The source anchor points to either
- a destination anchor, which is another region in the destination document
- a whole document, or
- a container object, i.e. a group of documents (multi-ended
link).
Because links in the Hyperwave Information Server are not statically
stored, as in classic hypertext data models (
Figure
3), many traditional problems are overcome, and many extra advantages gained.
These advantages are listed below:
Figure 3 :The Classic Hypertext Data Model
- Documents on the Hyperwave Information Server are stored in collections,
which can be viewed as hierarchical file systems. This allows you to see how
documents and collections are related. Also, because the collection hierarchies
and links are automatically maintained by the system, you can rest assured that
the document you visited the last time will still be accessible via the same
link the next time you want to access it. All documents in a collection are
listed when you navigate to that collection, so it is easy to see what
information exists on a certain topic. Hyperwave Information Server marks new
and updated documents with these words in red (
(new) and
(updated) ), making it easy for you to pick out new items from the
collection listing.
- Hyperwave Information Server provides excellent collaborative authoring
facilities. Many link consistency problems are avoided by the automatic link
management system. Multiple authors working on a set of documents need not
worry about links being broken when documents are deleted or moved. Hyperwave
Information Server automatically maintains these links to avoid frustration for
the user. This is particularly useful for large intranet sites, where there is
likely to be a lot of collaborative authoring.
- Also, documents are never "orphaned" on the Hyperwave Information Server,
because automatic link management ensures that links pointing to documents are
maintained even when the referring document is deleted or moved. When a
document is deleted, links pointing to it are marked as invalid and are not
merged into the corresponding documents (in other words, they become invisible
for ordinary users). When a document with the same name as the document that
was deleted is inserted into the server, the links are restored again.
- Another advantage of links being maintained automatically by the system is
that authors collaborating do not need to be given write rights to other
people's documents just to keep their links current. This allows for greater
security in the collaborative authoring area, as there is no danger of your
work being changed by someone else. Naturally, it also means less work for
everyone involved.
- Automatic link management allows for easy customization of views. Because
links are stored as separate objects on the Hyperwave Information Server, they
can also be assigned access rights. If a user has access to four out of five
documents in a sequence, the link to the fifth document will not even appear
for this user.
- Hyperwave Information Server manages to structure large amounts of
information, while still using hyperlink technology to its best advantage.
- Links are bi-directional. This means that it is possible to find the link
source from the link destination (this is a simple operation performed by the
repository). Users can navigate to the source from the destination, and the
system can generate nice looking link maps showing both incoming and outgoing
links around a given document (see
page
115).
- Source and destination anchors are objects, i.e. they have attributes such
as title, author, creation time, link type, etc. This means, for example, that
it is possible to search for links which were created by a given user during a
given time range.
- Links can be assigned individual access permissions, meaning that certain
links in a document can be defined to be visible and thus accessible only for
certain users or user groups. This is useful for presenting customized or
personalized information, where different users see different hyperlinks.
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