Some of my favourite quotes about classification are from Organising Knowledge:  Taxonomies, Knowledge and Organisational Effectiveness by Patrick Lambe.

Taxonomies are at the same time deceptively simple and fiendishly complicated. 

They are simple because they are absolutely basic to human consciousness, so everybody manipulates and creates them with great ease. Taxonomies are complicated because we use them for the most part unreflectingly – they are simply part of our mental and social background- and we use categorise in a hyge variety of ways, often in competing and inconsistent ways.

Different people with different tasks will order their knowledge assets differently to suit the tasks they have to do…

Our clients can and do categorise continually. They are confident about knowing how to sort things out . But they are not skilled at conscious, strategic organisation of their knowledge assets to suit collective tasks.

When it comes to information systems Lambe hits the nail on the head. Classification schemes are more than just search and retrieval tools. We need them to achieve a whole range of purposes including:

• Aggregation of content (grouping records together for business or evidential purposes)
• Browsing and navigation
• Access & security management
• Disposition management
• Filtering  and segmentation
• Managing provenance
• Reporting

Web research confirms a renewed interest in classification (taxonomies and metadata). There are a whole raft of new taxonomy and metadata products available, including those inbuilt into eCM systems like SharePoint 2010. However the marketing blurb suggests that the purpose of classification schemes is in the delivery of improved deliver search and retrieval.  Little is said about the theory and discipline of building classification schemes.

Both Lambe and Stewart in their books address the need to understand how different criteria are needed for different purposes. Lambe (Organising Knowledge, 2007) lists the following criteria (facets) used to classify content:

• Business activity i.e. functions, activities, processes, transactions
• Subject matter i.e. products, services, disciplines, domains, assets
• Names of people and organisations
• Aggregation i.e. cases
• Record or document type
• Geographic  location
• Time or sequence

The issue taxonomy developers face is that there is no single criteria which is able to realise all of the collective classification needs of the organisation.

The following matrix illustrates how different classification criteria (or facets) meet different needs. Some meet the aggregation and retrieval needs of business users, others meet compliance needs of the organisation. The art of building effective classification schemes is to identify all of the organisation’s classification needs and to weave them together into an IDEAL information architecture.