Lexicography is divided into two separate but equally important groups:
Practical lexicography is the art or craft of compiling, writing and editing dictionaries.
Theoretical lexicography is the scholarly discipline of analyzing and describing the semantic, syntagmatic, and paradigmatic relationships within the lexicon (vocabulary) of a language, developing theories of dictionary components and structures linking the data in dictionaries, the needs for information by users in specific types of situations, and how users may best access the data incorporated in printed and electronic dictionaries. This is sometimes referred to as 'metalexicography'.
There is some disagreement on the definition of lexicology, as distinct from lexicography. Some use "lexicology" as a synonym for theoretical lexicography; others use it to mean a branch of linguistics pertaining to the inventory of words in a particular language.
A person devoted to lexicography is called a lexicographer.
General lexicography focuses on the design, compilation, use and evaluation of general dictionaries, i.e. dictionaries that provide a description of the language in general use. Such a dictionary is usually called a general dictionary or LGP dictionary (Language for General Purpose). Specialized lexicography focuses on the design, compilation, use and evaluation of specialized dictionaries, i.e. dictionaries that are devoted to a (relatively restricted) set of linguistic and factual elements of one or more specialist subject fields, e.g. legal lexicography. Such a dictionary is usually called a specialized dictionary or Language for specific purposes dictionary and following Nielsen 1994, specialized dictionaries are either multi-field, single-field or sub-field dictionaries.
It is now widely accepted that lexicography is a scholarly discipline in its own right and not a sub-branch of applied linguistics, as the chief object of study in lexicography is the dictionary (see e.g. Bergenholtz/Nielsen/Tarp 2009).
Coined in English 1680, the word "lexicography" derives from the Greek λεξικογράφος lexikographos, "lexicographer", from λεξικόν lexicon, neut. of λεξικός lexikos, "of or for words", from λέξις lexis, "speech", "word", (in turn from λέγω lego, "to say", "to speak") and γράφω grapho, "to scratch, to inscribe, to write".
Practical lexicographic work involves several activities, and the compilation of well-crafted dictionaries requires careful consideration of all or some of the following aspects:
profiling the intended users (i.e. linguistic and non-linguistic competences) and identifying their needs
defining the communicative and cognitive functions of the dictionary
selecting and organizing the components of the dictionary
choosing the appropriate structures for presenting the data in the dictionary (i.e. frame structure, distribution structure, macro-structure, micro-structure and cross-reference structure)
selecting words and affixes for systematization as entries
choosing lemma forms for each word or part of word to be lemmatized
specifying pronunciations of words
labeling definitions and pronunciations for register and dialect, where appropriate
selecting equivalents in bi- and multi-lingual dictionaries
translating collocations, phrases and examples in bi- and multilingual dictionaries
designing the best way in which users can access the data in printed and electronic dictionaries
One important goal of lexicography is to keep the lexicographic information costs incurred by dictionary users as low as possible. Nielsen (2008) suggests relevant aspects for lexicographers to consider when making dictionaries as they all affect the users' impression and actual use of specific dictionaries.
Theoretical lexicography concerns the same aspects as lexicography, but aims to develop principles that can improve the quality of future dictionaries, for instance in terms of access to data and lexicographic information costs. Several perspectives or branches of such academic dictionary research have been distinguished: 'dictionary criticism' (or evaluating the quality of one or more dictionaries, e.g. by means of reviews (see Nielsen 1999), 'dictionary history' (or tracing the traditions of a type of dictionary or of lexicography in a particular country or language), 'dictionary typology' (or classifying the various genres of reference works, such as dictionary versus encyclopedia, monolingual versus bilingual dictionary, general versus technical or pedagogical dictionary), 'dictionary structure' (or formatting the various ways in which the information is presented in a dictionary), 'dictionary use' (or observing the reference acts and skills of dictionary users), and 'dictionary IT' (or applying computer aids to the process of dictionary compilation).
One important consideration is the status of 'bilingual lexicography', or the compilation and use of the bilingual dictionary in all its aspects (see e.g. Nielsen 1894). In spite of a relatively long history of this type of dictionary, it is often said[according to whom?] to be less developed in a number of respects than its unilingual counterpart, especially in cases where one of the languages involved is not a major language. Not all genres of reference works are available in interlingual versions, e.g. LSP, learners' and encyclopedic types, although sometimes these challenges produce new subtypes, e.g. 'semi-bilingual' or 'bilingualised' dictionaries such as Hornby's (Oxford) Advanced Learner's Dictionary English-Chinese, which have been developed by translating existing monolingual dictionaries (see Marello 1998).
Nielsen, Sandro (2008) "The effect of lexicographical information costs on dictionary making and use", in Lexikos (AFRILEX-reeks/series 18), pp. 170–189.
Nielsen, Sandro (2009): "Reviewing printed and electronic dictionaries: A theoretical and practical framework". In S. Nielsen/S. Tarp (eds): Lexicography in the 21st Century. In honour of Henning Bergenholtz. Amsterdam/Philadelphia: John Benjamins, 23-41.ISBN978-90-272-2336-4