"There are 15,331 files in the TC/CS. Most of the descriptor terms in the TC/CS are in plural form (i.e. cars). The thesaurus uses the convention: if you can answer the question 'how much ____?' (how much rain), then the term will be listed in the singular form. If you can answer the question 'how many ____?' (i.e. how many cars), then it will be listed in the plural form. If you are unsure, then append a '*' wildcard to the desired words in your search strategy; for example 'survey*'. There are 15,331 files in the TC/CS. Each of the descriptor terms in the electronic TC.CS are contained in a self-standing file. That is, a term such as 'thesaurus' is stored in a file named 'thesaurus.html', and the BT,WT,NT, etc. are external crosslinks contained in the file. In all cases, any CTCS descriptor can only point to a BT, GT or WT that is one level above, or a NT or PT that is one level below, or a RT or AT that is on the same level. There are 10 levels in this hierarchy, going from terms such as 'Knowledge' and 'Research' at the top level down to the nuts and bolts at the bottom level."