Information retrieval techniques span a spectrum from full-text search, which is a high-recall technique which makes little demand on the information representation, to knowledge-base query, which is a high-precision technique, which depends on a rich information representation.
Catalogs are databases structured for the purpose of browsing, searching, and generally organizing large volumes of related data, or more often: metadata. see also: design issues, where TimBL is writing about metadata again. 97-02-07 connolly
Metadata has two main functions:
WAIS through the Web - About Metadata
- to provide a means to discover that the data set exists and how it might be obtained or accessed; and
- to document the content, quality, and features of a data set and so give an indication of its fitness for use.
A catalog records is generally not a primary resource, but rather a surrogate, excerpt, abstract, or description giving some attributes of another resource. The question arises: whence comes the list of attributes? What's the expressive capability, structure, and meaning of attribute values?
A PICS label represents a set of category/value pairs, where the categories are part of a globally unique rating system. (While PICS 1.1 allows only for floating point values, an enhancement to accomodate string values is expected.)
PICS categories can serve as metadata attributes. Their meaning is given in the rating system. The structure of a PICS label is similar to:
Describing and Linking Web Resources for an architectural description of this metadata structure.
More complex structures can be accomodated by PICS extensions:
WEBDAV Meeting Notes:
Comment: So you will have to encode binary data? This is expensive. Response: Focus on the object-model. Is it complete? Consistent? Web Collections are just a convenient vehicle for expressing the object model; if there is a better way of expressing the model, we'll use it. Question: Who manages the link "types" (e.g., registration)? Answer: Core link types ("core" to implementing WEBDAV) are defined in the specification. Other "types" owned and managed various groups (e.g., Dublin Core). Namespace convention for link types is schema.(schema.type). Response: Take care! Define namespace requirements for links so that WEBDAV complies with the "Schema" work group (Chris Weider, Chair). Comment: Why be non-extensible w.r.t. the link definition? Allow other fields to be added to the core fields (source, dest, type). Comment: PICS is doing meta-data. The authors would be well advised to look at the PICS effort.