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long: in the music database, the composer page for Wolfgang Amadeus Mozart would list several hundred
corresponding pieces. This list would be somewhat cumbersome to view in a single web page. An intermediate
directory should be generated in cases where lists grow to long, containing links such as ``A-B'', ``C-D''... Also,
this could in many cases significantly reduce the time required for loading parts of lists, which is especially
important in the case of low Internet transmission rate.
Very short pages:
in a database, some tables can contain only very few short columns. However, presently a web page will be
generated for each table entry, unless it is an associative entity (see Section 6.3). This is not satisfying; a better
solution in this case would be to generate web pages containing more than one table entry, separated by a
distinguished border, such as a horizontal rule.
Code Translation:
In many applications short strings or single letter codes are used to code information (e. g. in the Music database,
``CH'' stands for choir, ``S'' for soloist). An automatic translation of such strings would improve the readability of
the hypertext. Adding a table Codetranslations (one-to-many relationship to Columns) to the meta base would
implement this concept.
7.2 Structural Improvements
Weak entities:
in our system catalog, the table Columns would be a weak entity: it cannot exist without its parent. All
information in entries in the Columns table should be added to the strong entity Tables. An analysis based on
3,000 tables in a large Austrian bank showed an average of 13 columns per table [Pönighaus 1993]: this means
that if we generated a system catalog browser we could save 13 web pages per entry in the table Tables (3,000
instead of 3,000 + 39,000 pages).
Denormalized data:
for performance reasons, data in practical applications are often denormalized: e. g. many-to-many relationships
are implemented via fixed-length arrays [Premerlani &Blaha 1994]. In order to generate appropriate hypertext
this situation must be recognized (by additional user input) and handled accordingly.
Slices:
[Isakowitz et al. 1995] introduced the concept of information slices in their
Relationship-Management-Methodology (RMM): splitting an entity into meaningful slices for presentation of
information, resulting in a separate web page for each slice of a table entry. In the present version of our
generator, all fields of a table would be presented in one page. There are situations where this is not satisfying;
we consider the integration of this concept into our meta base to be comparatively easy.
Dynamic HTML generation:
in our prototype the generation of the hypertext is done in batch mode, but the meta base can also be used for
dynamically generating SQL statements which extract the relevant data from the RDBMS. In this case the data
would always be up-to-date, which obviously is a requirement in many applications. The concepts discussed in
this work essentially remain unchanged for this task; in particular, there will be no need for any changes to the
meta base.
8 Conclusion
In this work we show an approach to the automatic generation of hypertext from relational databases using metadata.
Reverse engineering applied to relational databases proves to be applicable to this problem, since the referencing
information provided by the database system is ideally suited for automatically generating hypertext links between
documents for instances of entities. The use of a meta base which is extracted from the system catalog and which can be
augmented by the user allows for a flexible solution to the problems typically found in practical database applications.
In this text the method is applied to a database on music records. Interested readers are invited to take a look at the
music database at http://exaic.wu-wien.ac.at/~poenigh/platten/entry.htm.
References