ACTION-282 = Draft a finding on metadata architecture

Jonathan Rees and Michael Hausenblas, 14 January 2010

Previous version: metameta-20091202.html

1. Introduction

Metadata is a wide and amorphous topic and hence we have tried to identify relevant problem areas in a first step. In this memo we will focus on two metadata sub-areas: (i) data about documents, and (ii) data about core Web functions.

For each technology mentioned in respective sections below, we provide a concrete, real-world example that illustrates its usage.

2. Data About Documents

As of Metadata on the Web: A survey, metadata in the strict sense. For the sake of argumentation and in the scope of this note, we define metadata in the traditional sense used in information science: descriptive information about document-like things. We intentionally stretch the semantics of word 'document' to construe it very broadly. So, not just books and articles but also static Web pages, audio recordings, images, videos, and other similar resources are covered by the word 'document' inhere. Metadata architecture then applies to the creation, maintenance, transmission, and application of this particular kind of information. This is of interest to W3C because so much of the value of the Web is tied up in this sort of object.

Dublin Core

SVG Metadata


3. Data About Core Web Functions

Core Web functions in the scope of this document are all functions of the Internet-based, REST eco-system aka the Web. This includes, but is not limited to, data about transfer, access, provenance, HTTP, authentication, Web services, discovery, etc.

Ontology for Media Resource 1.0

Test Metadata


Well-known URIs


4. Background

In more or less chronological order:

  1. Metadata on the Web: A survey Feb 2009
  2. Discussion of first-party-provided metadata (as opposed to metadata from other sources). This has mostly fallen under ISSUE-62 (303, LRDD)
  3. Larry Masinter email on July 21 announcing ISSUE-63: Metadata Architecture for the Web, closing ACTION-254. This frames the issue, saying what the components of any metadata architecture ought to be.
  4. Steve Rowat's writings:
    1. US patent 6782394 "Representing object metadata in a relational database system"
    2. email to www-tag 21 August "Goals of a W3C-mediated Global Metadata System"
    3. email to www-tag 21 Sep "Ten Use-Cases of Individual Content Authors Requiring Rights/Commerce Metadata"
    I found these to be interesting as they raise the issue of attaching metadata to resource parts such as sections, passages, tracks, time intervals. This relates to RDFa which (among other things) supports metadata referring to parts of XHTML documents, and our previous discussion of URIs for video segments.

What follows is the entire collection of 'old' stuff, incl. JAR's draft from 2010-01-07 for the road ahead. It will be step-by-step moved to the sections above.

Possible areas of focus

"Metadata" is a huge, amorphous topic and it is important that we attempt to focus on a single problem or problem area. I have identified the following possibilities:

  1. Null hypothesis: Metadata is just like any other kind of data, such as melting points of chemical substances. Data is of great architectural interest to W3C. However, the correct treatment of metadata is just a special case of the correct treatment of data, so metadata per se is of no special interest to W3C.
  2. Data about documents: We define metadata in the traditional sense used in information science: it is descriptive information about document-like things. We abuse the word "document" to construe it very broadly - so not just books and articles but also static web pages, audio recordings, images, video, and other similar resources. Metadata architecture then applies to the creation, maintenance, transmission, and application of this particular kind of information. This is of interest to W3C because so much of the value of the Web is tied up in this sort of object. [Note: JAR doesn't like stretching words like "document" in this way, but this term was adopted as a compromise in a discussion on this subject.]
  3. Data about Web plumbing: Many discussions about metadata drift away from data about documents and into adjacent ontological territory involved with making the web work. For example, data about people, organizations, hosts, network services, and other dynamic resources is interesting because all of these entities participate in creating the value of the web - the interest goes beyond their role in creating and consuming documents. (Examples: WSDL, XRD.) While it is correct to say that such data is not metadata, doing so does not satisfy the thirst for a uniform treatment of such plumbing-related information.

For the next draft (in progress), I propose looking at the both of the latter two, eventually either dropping one or, if necessary, splitting into two documents.

An architectural document is most successful when it starts from problems and applications, not technologies. If we look at the protocols and formats that are often discussed in the context of metadata (XML, OWL, POWDER, Link: header, and so on), we find that many of them are applicable to any of the above concentration areas (data-generally, data-about-documents, data-about-web-plumbing), and this fact helps explain why discussions can get so confusing. I propose that for the next draft discussion of any technologies or other considerations that seem to be independent of application area be relegated to a late section or appendix to help make its independence clear.

TBD: (1) Organize this document into three parts (a) data-about-documents (b) data-about-web-plumbing (c) common technological base. (2) For each format or technology mentioned in "What deployments / use cases are inspirational?" below, and in the earlier survey, provide a link or snippet that concretely illustrates the format, and locate one or more user-facing applications that make use of that format. E.g. for Dublin Core, find some actual "wild type" metadata that uses the DC vocabulary, and find at least one application that puts DC metadata to some interesting use (indexing, browsing, etc.).

Why should the TAG get into this?

Why should the TAG care about metadata?

What is the division of responsibility between TAG and others (e.g. W3C working groups)?

What could we possibly do? We're not a WG.


For further research:

Does metadata have any special role on the web (as compared to other kinds of content)?

Yes, metadata makes the data (and therefore the Web) more valuable in particular ways that both promote interoperability and benefit from it.

Is there a problem? In what ways is metadata on the web less webby (connected, open, inclusive) than it ought to be?

Not enough of it (example?) - poor incentives for creating it

Difficult to deploy

Hard to validate

A lot of what's there is closed, e.g.

Difficult to use at scale

Being a master consumer of metadata is complicated (XMP, GIF, <link>, LRDD, 303, RDFa, ...)

Doubt and uncertainty regarding data identity

Unclear lines of authority, thus difficult to evaluate for trustworthiness (but how is this different from any other content on the web?)

How to consistently identify people, organizations, places (organize bookmarks by author, photos by place)

What metadata do we care about?

Is there such a thing as data that is not metadata? Metadata that is not data? Can non-data have metadata? If X is about Y, does that mean X is in scope of this project, or is X only in scope when Y is data?

Are OpenID and XRD a metadata use case, or just application-related data?

Is RDF nose-following (linked data) a metadata use case, a world unto itself, or an intersecting world?

Should we focus our attention on particular metadata profiles (e.g. Dublin Core), or on the meta-metadata problem (bibliographic would be a special case, offers to sell might another, audio another, etc.)?

Is "metadata" even the right word to cover this project?

What deployments / use cases are inspirational?

Both private and public, that is. Figure out business models, especially for the more public sources.

What potential technical opportunities are there?

Things someone might do in RDF-land to advance web metadata:


Does "metadata architecture" make sense? Is it something to be discovered (empirical), designed (invented), or some of each?

Is anything different now compared to 10 years ago when RDF and Dublin Core were published?

The Metadata Activity Statement (1998) is worth a look.