# Element Expression¶

## Introduction¶

Element Expressions is a language for exploring and querying the AlvisNLP Corpus. It can be used to test features, count elements, retrieve annotations with certain characteristics, etc. This language shares a lot of common points with XPath, so if you are, or become, familiar with XPath, then good for you. You may find the following pages also useful:

• Element Expression Examples contains several examples of expressions in increasing order of trickiness;
• Shell describes the AlvisNLP/ML Shell that you can use to train yourself to write expressions.

## Context Element¶

Expressions are evaluated within a context that includes an element. The context element can be one of the following:
• the corpus
• a document
• a section
• an annotation
• a relation
• a tuple

Some expressions are independent of the context element; their evaluation does not depend on it (for instance arithmetic operators). However the most useful expressions depend on the context element, for instance the evaluation of a feature value expression obviously depends on the context element. Wherever an expression is expected, for instance as a module parameter, the context element sould be documented.

## Evaluation types¶

An expression can be evaluated as on of four types: boolean, number, string or element list. The evaluation type should be documented along with the context element.

### Scalar types¶

#### Boolean¶

The boolean type has two values: false and true.

#### Double¶

The double type is a double precision 64-bit floating point number (Java double).

#### Integer¶

The integer type is a 32-bit signed integer (Java int).

#### String¶

The string type is a 16-bit unicode character sequence (Java String).

### Element list¶

The element list type is an ordered collection of elements. In most cases elements in an element list are of the same type (all Annotations or all Documents etc.).

### Type coercion¶

The majority of expressions have a priviledged or primary evaluation type, however they can be evaluated into any other type. The value is computed using the following type coercion rules:

 boolean number string list boolean false=0, true=1 false="false", true="true" empty list number 0=false, otherwise true decimal notation string empty list string ""=false, otherwise true decimal conversion, 0 if string is not number empty list list empty=false, otherwise true element count concatenation of static features

Some expressions have specific coercion rules.

## Operator precedence and associativity¶

The following operators are listed in descending order of precedence. The precedence can be overriden with parentheses.

 Operators Associative if then else no or yes and yes not no == != < > <= >= ?= ^= =^ =~ in any no ^ yes + - yes * / % yes unary - no pipe yes . yes

## Syntax for names¶

Some expressions require a name (feature key or layer name for instance). Names are single quote character sequences. The quotes can be omitted if all the following conditions are met:
• all characters are alphabetic (A-Za-z) or undescore (_)
• the name is different from any reserved word:  after and any arg args before boolean contents corpus delete document documents double elements else end false feat fun if in int inside layer length not new or outside overlapping relation relations section sections span start string then true tuples

Note that names and keywords are case-sensitive. All keywords are all lowercase.

## Expression reference¶

In the following sections each available expression is described. The usage of the expression is given in preformatted paragraphs with the following conventions:

  EXPR         uppercase words are variable parts of the expression construct, they are meant to be replaced either by sub-expressions, names or constants
layer        lowercase words are keywords
( ) . + :    all other sylmbols are operators, parenthes or a column, they are part of the expression syntax


If there is a preferred type for the expression, then this type is specified between brackets in the expression name.

#### Boolean constant [boolean]¶

  false
true


#### Integer constant [integer]¶

  [0-9]+


#### Double constant [double]¶

  ([0-9]*\.)?[0-9]+


#### String constants [string]¶

  "..."


String constants are double quoted character sequences. The usual Java escape sequences apply.

#### Boolean operators [boolean]¶

  LEFT and RIGHT
LEFT or RIGHT
not EXPR


LEFT, RIGHT and EXPR are evaluated as booleans with the same context element.
Binary boolean operator evaluation is short-circuited.

#### General comparison [boolean]¶

  LEFT == RIGHT
LEFT != RIGHT


LEFT and RIGHT are evaluated as the same type with the same context element. If LEFT is an expression of scalar type, then its type is used. Otherwise, the type of RIGHT is used.

#### Number comparison [boolean]¶

  LEFT < RIGHT
LEFT > RIGHT
LEFT <= RIGHT
LEFT >= RIGHT


LEFT and RIGHT are evaluated as doubles using the same context element.

#### String comparison [boolean]¶

  LEFT ?= RIGHT
LEFT ^= RIGHT
LEFT =^ RIGHT

LEFT and RIGHT are evaluated as strings using the same context element.
Meaning of operators:
 ?= contains ^= starts with =^ ends with

#### String concatenation [string]¶

  LEFT ^ RIGHT


LEFT and RIGHT are evaluated as strings with the same context element.

#### Regexp match¶

  TARGET =~ "PATTERN"


TARGET is evaluated as a string with the same context element. "PATTERN" is a string constant containing a regular expression in Java syntax
If evaluated as a boolean, then this expression returns either the target matches the pattern.
If evaluated as a number, then this expression returns the number of non-overlapping matches of the pattern in the target.
If evaluated as a string, then this expression returns the first match of the pattern in the target.
If evaluated as an element list, then this expression returns an empty list.

#### Arithmetic [double]¶

  LEFT + RIGHT
LEFT - RIGHT
LEFT * RIGHT
LEFT / RIGHT
LEFT % RIGHT


LEFT and RIGHT are both evaluated as numbers with the same context element.

#### Unary minus [double]¶

  - EXPR


EXPR is evaluated as a number with the same context element.

#### Dictionary lookup [boolean]¶

  EXPR in "FILE"[:"ENCODING"]


EXPR is evaluated as a string with the same context element. "FILE" is a string constant containg the path to a dictionary file. "ENCODING" is a string constant containing the name of the dictionary file character set. If the encoding is omitted, UTF-8 is assumed.
The dictionary file must contain one entry per line. This expression returns true if and only if the dictionary contains the first operand.

#### Feature [string]¶

  @KEY


KEY is a name. This expression returns the last value of the feature with key KEY of context element.
If this expression is evaluated as a boolean, then it returns true if and only if the context element has a feature with key KEY, even if the feature value is an empty string.

#### Any feature value equals [boolean]¶

  any KEY == EXPR


KEY is a name. EXPR is evaluated as a string with the same context element.
This expression returns true if at least one of the values of the feature with key KEY in the context element equals EXPR.

#### Annotation positions [integer]¶

  start
end


These expressions return respectively the start and end positions if the context element is an annotation. Otherwise it returns 0.

#### Element length [integer]¶

  length


If the context element is an annotation, then this expression returns its length.
If the context element is a section, then this expression returns returns the length of the section's contents.

#### Section contents [string]¶

  contents


If the context element is a section, then this expression returns its contents. Otherwise the empty string is returned.

#### Conditional¶

  if CONDITION then TRUE else TRUE


CONDITION is evaluated as a boolean with the same context element. If the result is, then TRUE is evaluated as the same type with the same context element. Otherwise FALSE is evaluated as the same type with the same context element.

#### Union [list]¶

  LEFT | RIGHT


LEFT and RIGHT are evaluated as element lists with the same context element. This expression returns the concatenation of the two results.
Elements in the result list are not reordered. Duplicate lements remain.

#### Path¶

  LEFT . RIGHT


LEFT is evaluated as an element list, then each element of the result is used as the context element to evaluate RIGHT.
If this expression is evaluated as a boolean, then it retuns true if any evaluation of RIGHT as a boolean is true.
If this expression is evaluated as a number, then it returns the sum of all successive evaluations of RIGHT as a number.
If this expression is evaluated as a string, then it returns the concatenation of all successive evaluations of RIGHT as a string.
If this expression is evaluated as a list, then it returns the concatenation of all successive evaluations of RIGHT as a list.

Element navigation expressions returns elements according to a navigation specification. The following subsections describe each available specification.
A specification can be followed by filters and ranges. The order of filter and ranges specifies the order in which they are applied. If a range follows a filter, then range is applied after the filter.

#### Filters¶

  SPEC [ EXPR ]


SPEC is a navigation specification. EXPR is evaluated as a boolean with the current element as the context element.
The expression returns the list of elements for which EXPR was evaluated as true.

#### Ranges¶

  SPEC { N }
SPEC { N : M }
SPEC { : M }
SPEC { N : }


SPEC is a navigation specification. N and M are integer constants.
The returned list is a sublist of the list returned by SPEC: |N|a singleton list with the @N@th element| |N : M|the sublist from the @N@th (inclusive) to the @M@th (exclusive) elements| |: M|the sublist from the start to the @M@th element (exlusive)| |N :|the sublist from the N@th element (inclusive) to the end|List indexes are zero-based: @0 is the first, 1 is the second, etc. If N or M are negative, then the length of the list + 1 is added to their value: -1 is the last (inclusive).
If the indexes are out of the list boundaries then the index is "cropped".

#### Self¶

  \$


This expression returns the context element.

#### Element corpus¶

  corpus


This expression returns the currently annotated corpus.

#### Element document¶

  document


This expression returns a singleton list containing the document to which the context element belongs.
If the context element is a document, then this document is returned.
If the context element is the corpus, then the empty list is returned.

#### Element section¶

This expression returns a singleton list containing the section to which the context element belongs.
If the context element is a section, then this section is returned.
If the context element is the corpus or a document, then the empty list is returned.

#### Tuple relation¶

  relation


If the context element is a tuple, then this element returns a singleton list with the relation to which the tuple belongs. Otherwise it returns the empty list.

#### Corpus documents¶

  documents
documents : ID


ID is a name. If the context element is the corpus, then this expression returns a singleton list containing the document with the identifier ID. If ID is omitted, then this expression returns a list containing all documents in the corpus.
If the context element is not the corpus, or there is no document in the corpus, or there is no document with the specified identifier, then this expression returns an empty list.

#### Document sections¶

  sections
sections : NAME


NAME is a name. If the context element is a document, then this expression returns a list containing all sections in the document with the name NAME. If NAME is omitted, then this expression returns all sections of the document.
If the context element is not a document, or there is no section in the document, or there is no section with the specified name, then this expression returns the empty list.

#### Section annotations¶

  layer
layer : NAME


NAME is a name. If the context element is a section, then this expression returns a list containing all annotations in the layer named NAME. If NAME is omitted, then this expression returns all annotations of all layers of the section.
If the context element is not a section, or there is no layer with the specified name, or there is no annotation in the section, or the layer with the specified name is empty, then this expression returns the empty list.

In all cases, the list of annotations is sorted by standard order (increasing start, then decreasing end) and duplicates are removed.

#### Section relations¶

  relations
relations : NAME


NAME is a name. If the context element is a section, then this expression returns a singleton list containing the relation in the section with the name NAME. If NAME is omitted, then this expression returns all relations of the section.
If the context element is not a section, or there is no relation in the section, or there is no relation with the specified name, then this expression returns the empty list.

#### Relation tuples¶

  tuples


If the context element is a relation, then this expression returns a list of all tuples of the relation. Otherwise it returns the empty list.

#### Tuple arguments¶

  args
args : ROLE


ROLE is a name. If the context element is a tuple, then this expression returns a singleton list containing the annotation which is the argument of the tuple with the role ROLE. If ROLE is omitted, then this expression returns a list containg all arguments of the tuple (in no particular order).
If the context element is not a tuple, or the tuple has no arguments, or if the tuple does not have an argument with the specified role, then this expression returns the empty list.

#### Reverse tuple lookup¶

  tuples : RELATION
tuples : RELATION : ROLE

RELATION and ROLE are names. If the context element is an annotation, then this expression retuerns a list containing all tuples that satisfy all the following conditions:
1. the tuple pertain to the relation with name RELATION in the same section
2. the annotation is the argument of the tuple with role ROLE, if ROLE is omitted, then the annotation is an argument of the tuple regardless of the role
If the context element is not an annotation, or the section does not contain a relation with the specified name, then this expression returns the empty list.

#### Annotation siblings¶

  after : NAME
before : NAME
inside : NAME
outside : NAME
overlapping : NAME
span : NAME


If the context element is an annotation, then this expression returns a list of annotations in the layer with name NAME in the same section. The annotations included in the result list depend on the keyword:

 after start after the context annotation end before end before the context annotation start inside fully included in the context annotation span outside fully includes the context annotation overlapping overlaps (broad sense) the context annotation span exact same span as the context annotation

If the context element is not an annotation, or the section does not have a layer with the specified name, then this expression returns the empty list.
In all cases, the returned list is sorted in standard order.

### Side-effect expressions¶

Side-effect expressions affect the corpus data structure. Only some modules allow actions inside an expression; refer to the module documentation.

#### Element creation¶

  new : document ( ID )
new : section ( NAMEEXPR , CONTENTS)
new : section : NAME ( CONTENTS )
new : relation : NAME
new : tuple
new : LAYER ( START , END )
new : LAYER ( ANNOTATIONS )


Expressions that start with new: create a new element and return it. The type of the element depends on the next functor. The created element is attached to the context element. If the context element is not of the adequate type then the expression does nothing, and returns nothing.
ID is an expression evaluated as a string. If the context element is the corpus, then new:document(ID) creates a document with the specified identifier. If the corpus already contains a document with the specified identifier, then an error is issued.
NAMEEXPR and CONTENTS are expressions evaluated as strings. If the context element is a document, then new:section(NAMEEXPR,CONTENTS) creates a section with the specified name and contents.
NAME is a name: new:section:NAME(CONTENTS) allowes to create a section by specifying the name without an expression.
If the context element is a section, then new:relation:NAME creates a relation with the specified name.
START and END are expressions evaluated as integers. If the context element is a section, then new:LAYER(START,END) creates an annotation with the specified positions, then adds it to the specified layer.
ANNOTATIONS is an expression evaluated as a list of elements. new:LAYER(ANNOTATIONS) creates an annotation that covers all annotations of the same section in ANNOTATIONS, then adds it to the specified layer.

#### Set argument¶

  arg : ROLE ( ARG )


ROLE is a name and ARG is an expression evaluated as a list of elements. If the context element is a tuple, the this expression sets the argument with the specified role to the first annotation in the result of ARG. If the evaluation of ARG does not yield any annotation, then this expression does nothing.
This expression always return the context element, so different arguments can be chained by paths.

#### Set feature¶

  feat : KEY ( VALUE )


KEY is a name and VALUE is an expression evaluated as a string. This expression adds a feature with the specified key and value to the context element.
This expression always return the context element, so different arguments can be chained by paths.

#### Delete element¶

  delete


This expression deletes the context element. The deletion is permanent. The corpus cannot be deleted.

  add : NAME


If the context element is an annotation, then this expression adds it to the layer named NAME.

#### Remove from layer¶

  remove : NAME


If the context element is an annotation, then this expression removes it from the layer named NAME.

### Library function call¶

  lib : FTOR1 : ... : FTORn ( ARG1 , ... , ARGm )


This expression calls a library function with arguments ARG1, ..., ARGm.