Metadata is ubiquitous - the title of your favourite book, the label on your shopping item, the caption on your holiday photograph and the geographical coordinates of you current location are all metadata. Whilst people, places, objects and events are real objective (verifiable) facts, the metadata that describes them is a social construct hence could be intensely subjective, says Richard Gartner in his book. As discussed in the book, metadata is purposeful, contextual and subjective. He tells us that metadata is an approximation to the things it represents. In this succinctly written book, Richard Gartner weaves a historical thread of the practice of describing information artefacts and resources using metadata - he does so by tracing its historical and multi-disciplinary roots from librarianship to computer science, from GIS to business, from authoritative standards to bottom-up folksonomies.

Gartner writes that “One feature of metadata that is often forgotten is that it is a human construct and not found in nature. The shape of metadata is designed by human beings for a particular purpose or to solve a particular problem, and the form it takes is indelibly stamped with its origins. There is nothing objective about metadata: it always makes a statement about the world, and this statement is subjective is what it includes, what it omits, where it draws its boundaries and in the terms it uses to describe it”.

Metadata, as Gartner aptly illustrates, is central not only to library work but also to almost every other area of business that involves organising, finding, managing and archiving information. Who made that phone call, to whom, on which particular day and on what subject matter? That layer of additional data, that about-ness is what we call metadata. Meta in Greek refers to after, beyond or about things, events or people (as in meta-physics, meta-theory, or even “meta-metadata”). He admits the meaning of metadata goes well beyond its catchy but circular definition of “data about data” and he offers excellent practical examples from city maps to intelligence data gatherings.

Gartner, who taught metadata at King’s College London, worked for many years in the Bodleian Library at Oxford University and currently digital librarian at the Warburg Institute in the University of London, argues that the chief business of libraries, whether they call it cataloguing, classification, information organisation or discovery systems, is metadata. Metadata helps us find things, ascertain provenance and provide context. The book provides an overview of existing metadata approaches and standards such as MARC, Dublin Core, MIX and EAD. This book also offers a succinct history of metadata and discusses emerging metadata approaches.

The book discusses topics covering taxonomies, controlled vocabularies, faceted classification, ontologies and folksonomies. It addresses a shift from strict hierarchal information organisation systems to networked and interlinked metadata systems. He cites examples such as FOAF and SKOS – which use RDF to represent and encode metadata. As Gartner explains metadata has three fundamental components – semantics (metadata fields), syntax (example XML) and content rules. The book provides a succinct historical backdrop of how metadata came to develop and current applications of Linked Data and crowdsourcing projects.

Gartner cites Russell Ackoff’s DIKW (Data, Information, Knowledge and Wisdom) hierarchy – and argues metadata helps us create the necessary links between these components. He notes “human knowledge is built on ‘aboutness’ and it is through our interpretation of what the world is ‘about’ that most of our intellectual endeavours are based. Without metadata we cannot have knowledge".

The author gives credit to the pioneers of cataloguing and metadata work – from Kallimachos who organised a list of the Pinakes (tablets) at the Library of Alexandria to Thomas James of the Bedleian Library in Oxford, Panizzi (the British Museum), Dewey, Ranganathan, Tim Berners-Lee and many others. In his chapter on democratising metadata, Gartner notes the challenges to harness user-generated metadata along with that of expert-created metadata. “The answer seems to be working out some way of filtering it, honing it down so that it becomes usable and let us find what we want. This is the model presented in a recent book by Getaneh Alemu and Brett Stevens; they use the epithet ‘enrich then filter’ for a model that should let us have the best of both worlds, diverse, vibrant metadata and focused, relevant search results. Their idea is that we encourage metadata from all sources: the ‘expert’-created records that have been the norm for so long and community-generated ones that come from anyone willing to provide it. We then filter this rich but confusing and always changing body of metadata as and when we need it to meet our requirements”. Gartner concurs that expert-created and user-generated metadata are complementary. He sees no reason to throw one or another.

He cites several examples of crowd-sourcing projects such Galaxy Zoo, also called a citizen science project, where hundreds of thousands volunteers from around the world contributed in the identification and classification of planets and astronomical objects from a deluge of satellite images; and Ancient Lives where online volunteers help transcribe ancient Greek papyri.

This book can be read by both technical and non-technical people as it uses a rather accessible language. Metadata makes information finding easier. This is an excellent read and I highly recommend it to my colleagues and friends. As Gartner notes “metadata, as always throughout its history, never stands still” and his book is an excellent addition to such a dynamic and an ever changing field. And since metadata is a social construct, as the author argues, we should approach it with a pragmatic, purposeful, contextual and subjective viewpoint. Yes, I agree with the author that metadata has helped shape "knowledge from antiquity" to the present day of the Semantic Web and yes "it represents our desire to make sense of the world, to know what it, and we, are 'about'".