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Chapter 5
Metadata
5.1 Definition
Metadata includes a description and control information about data, or simply data about data. The
theory of this system is for each file to be uniquely identifiable by its metadata, in a more common
hierarchical tree based filesystem, this would be achieved by a file’s path and name. By storing each
file with its own metadata stored in an index, any group of files on the system can be defined by a view
query. In a tree based file system, files may be sorted by the user and organised into a folder structure.
This is an effective method of organising files if the user is careful in his saving of files. The user then
should be capable of retrieving any file from his logical file structure. However if the user wanted to
retrieve a group of documents defined by some parameter that isn’t part of the definition of his folder
structure this would be very difficult to do.
Having all the metadata for each file indexed means that arbitrary views on the files in the system
can be created enabling browsing of the available files by any attribute.
5.2 Technologies
There are three classes that metadata falls in to:
• Author Supplied. When the author publishes a document, he may add metadata to it. Common
attributes might be the author’s name, the title, some keywords, the validity period and date
published.
• Third-Party Supplied. If documents are being added to an information retrieval system or digital
library, there may be a group of metadata authors that read the documents and write metadata in
order to categorise them.
• Automated Derived. Much of this metadata can be extracted from a well structured data type.
SGML documents being one example, other media such as images and audio are difficult to derive
metadata from their binary content. It is currently unfeasible for a piece of software to derive a
description of the contents of an image or audio file. Much research is being done in this area
including work here at Imperial in The Multimedia Information Retrieval team. However this is
beyond the current scope of the project.
We will handle the first two types of metadata in the system but also keep the framework extensible so
that future work on automated metadata extraction can be added in a modular fashion to extend the
system.
5.2.1 Author Supplied Metadata
This data is attached to the file in a file type dependent manner. In order to extract this data into common
set of attributes, various filters will be written to handle the extraction of the data from the different
formats.
In a public or widely accessible system author metadata unfortunately cannot always be relied on for
an accurate description of the contents of the document. It is common for authors to add very common
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