====== The DQD Query Language ======

LCP's query language DQD (Descriptive Query Definition) follows the idea of Entity-Relationshop models. Entities sets are defined by logical formulae on properties and relations between them. The query engine then searches for those constellations inside the corpus or corpora selected. Along the lines of first order logic, quantors can be employed to enforce the existence or non-existence of constellations.

Every query needs to specify at least one result set, which is either a (plain) list of entities comprising the query matches, a statistical or a collocational analysis. T


===== Introduction =====

In a text corpus with standard annotations (viz the [[https://universaldependencies.org/format.html|CoNLL-U format]]), a simple query for the occurrence of the word "dogs" would look like this:
<code dqd>
Segment s

Token t
    form = "dogs"

Result => plain
    context
        s
    entities
        t
</code>



==== Instanciation and Scopes ====

Entities are instanciated by providing the entity name followed by a (unique) handle, which can be used to reference the entitiy. 
By instanciating an entity, it is by default existantially quantified and its scope ranges from its instanciation to the end of the queury. Exceptions are negative existential quantification and entities inside sequences with repetitions (see below).
<code dqd>
Segment s
</code>
//An entity of type "Segment" (sentence segment) is instanciated with the handle "s" assigned.//
The part-of operator ''@'' requieres the subsequently instanciated entity to be part of the previously instanciated entity which is referred to by its handle.
<code dqd>
Segment s

Token@s t
</code>
//An entity of type "Token" is instanciated with the handle "t" assigned. It is required to be part of the sentence segment "s"//



==== Dimensions ====

Entities are tied to at least one dimension. Three dimensions are available in LCP:

  - **Stream** -- 
  - **Time** -- 
  - **Space** -- 





===== Quick Reference =====

<wrap #entity />
==== Entities ====

Entities are defined in the [[|Corpus Template]]. Though aleatory names can be used, we use //Document// for documents, //Segment// for sentence segments and //Token// for tokens in the examples. Entities are expected to start with an uppercase character.


<wrap #attribute />
==== Attributes ====

Attributes are also defined in the [[|Corpus Template]] and thus their naming is free for a corpus creator to define. As a standard set, we use //form// for word forms, //lemma// for lemmas, //upos// for [[https://universaldependencies.org/u/pos/all.html|Universal part-of-speech tags]], and //morph// for [[https://universaldependencies.org/u/feat/all.html|Universal features]]. Attributes stored as [[|Meta Data]] is mapped to entity attributes unless a native attribute with the same name exists. In that case, the meta attribute needs to be explicitely referenced.