To understand indexing, one of the things you need to understand is the concept of "context".

 

From the Shorter Oxford English Dictionary:

 

Context, noun

 

3. The part or parts immediately preceding or following a passage or word as determining or helping to reveal its meaning; the surrounding structure as determining the behaviour of a grammatical item, speech, sound, etc.  (16th century).

 

>b figurative: Ambient conditions; a set of circumstances; relation to circumstances.  (19th century).

 

[Latin contextus from context- past participle stem of contexere weave together, formed as CON- + texere weave.]

 

As part of understanding "context", it is also important to understand something about the way we think.  Let's take for instance the word "valve". When this word is said (or written) alone (i.e. taken OUT of context), some people might think of a water faucet, others might think of the generic idea that it is something that regulates flow on some channel (e.g. air, water), and it is not clear at all what actual concept is meant.  What kind of valve?  How big is it?  Where is it?  But if you give it context, then you can get very precise about what comes to mind when the reader (or listener) encounters it.  Example:

 

 

 

 

Note that I just conveyed the concepts of 5 very different kinds of valves, simply by supplying their context.  Note also the impact of using context.  Now, instead of different people getting different ideas about what one is talking about, it is likely that every single person will end up with the same understanding of what is meant by the word "valve" when its context is included.  This is the role context plays in conveying ideas to others.  It's not just "nice to have", it's vital to getting ideas conveyed and understood.  Notice that in the above example, context was provided by using one, or at most a small number of words.

 

 

 

As you can see from the above demonstration, context is a crucial component of conveying any ideas in a way that they can be understood.  This is true whether one is talking to another person, talking in front of an audience, writing an article, a book, documentation for a software library, or truly any type of communication in which ideas need to be conveyed to people and understood.  This includes the creation of high-quality indexes for documents, large and small.

 

 

 

Note that one of the tools I used in these contexts is hierarchy.  If we think of hierarchy as a "tree structure", the closer one gets to the "leaves" in the tree, the narrower the concept becomes.  Conversely, the closer one gets to the "trunk" of the tree, the broader the concept is.  So we consider that the "narrower" concepts are "contained by" the broader concepts.  And in this structure, the relationships between them are shown by the broader concepts being listed first, and the narrower concepts being listed with the broader concepts, but their indentation level shows that they are contained by with the broader concept, and are themselves narrower in scope.

 

Hierarchy in context is one of the powerful tools that can make an index more useful to your readers, and used well, will enable your readers to find things they are looking for quickly.