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<ol class="chapter"><li class="expanded affix "><a href="introduction.html">Introduction</a></li><li class="expanded "><a href="filters.html"><strong aria-hidden="true">1.</strong> Filter Grammar</a></li><li class="expanded "><a href="queries.html"><strong aria-hidden="true">2.</strong> Query Grammar</a></li></ol>
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<h1 class="menu-title">Mercator Parser</h1>
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<h1><a class="header" href="#introduction" id="introduction">Introduction</a></h1>
<p>To support volumetric queries for Mercator, a new domain-specific language (DSL) was created.</p>
<p>ANTLR was used to write and test the SDL, to check it stays simple
to parse and and fast to execute. The actual <a href="https://epfl-dias.github.io/mercator_parser/">parser</a> and interpreter is
defined in rust, using <a href="https://docs.rs/lalrpop/0.18.1/lalrpop/">LALRPOP</a>.</p>
<h1><a class="header" href="#filter-grammar" id="filter-grammar">Filter Grammar</a></h1>
<p>You will find below the definition of this SDL, for filtering data
from the index.</p>
<h2><a class="header" href="#filtersg4" id="filtersg4">filters.g4</a></h2>
<pre><code class="language-antlr">grammar filters;
/**********************************************************************/
/* SELECTING / FILTERING DATA */
/**********************************************************************/
filters
: bag_expression
;
/* All these expressions generate bags. */
bag_expression
// Bag Operators
: distinct
| filter
| complement
| intersection
| union
| bag
// Spatial Operators
| inside
| outside
//| shape
;
/**********************************************************************/
/* BAG OPERATORS */
/**********************************************************************/
distinct
: 'distinct' '(' bag_expression ')'
;
/* Returns all the points which are NOT part of the bag. */
complement
: 'complement' '(' bag_expression ')'
;
/* Returns points which are part of both left and right sets. */
intersection
: 'intersection' '(' bag_expression ',' bag_expression ')'
;
/* Returns points which are either part of left or right sets
* (or both). */
union
: 'union' '(' bag_expression ',' bag_expression ')'
;
/* Filters point so that points part of the resulting bag respect
* the predicate. */
filter
: 'filter' '(' ( bag_expression | predicate ( ',' bag_expression )? ) ')'
;
predicate
: less
| greater
| equal
| str_cmp
| not
| and
| or
;
less
: '&lt;' '(' position_expr ',' position ')'
;
greater
: '&gt;' '(' position_expr ',' position ')'
;
equal
: '=' '(' position_expr ',' position ')'
;
not
: '!' '(' predicate ')'
;
and
: '&amp;' '(' predicate ',' predicate ')'
;
or
: '|' '(' predicate ',' predicate ')'
;
/* Arbitrary bag of positions. */
bag
: 'bag' '{' bag_expression (',' bag_expression )* '}'
;
/**********************************************************************/
/* SPATIAL OPERATORS */
/**********************************************************************/
/* Faces | vertices are included to allow selection on a pure plane or
* boundary.
*
* For example:
* intersection(outside(hyperrectangle{[0,0], [1,1]},
* inside(hyperrectangle{[0,0], [1,1]})
* will be true for any point lying EXACTLY on a face, corner or edge
* of the cube [0,0], [1,1].
*/
/* Returns the set of points outside the shape, (face included) */
outside
: 'outside' '(' shapes ')'
;
/* Returns the set of points inside the shape, (face included) */
inside
: 'inside' '(' shapes ')'
;
/* Returns the set of positions inside the shape, (face included) */
shape
: 'shape' '(' shapes ')'
;
/**********************************************************************/
/* SHAPES */
/**********************************************************************/
shapes
: point
| hyperrectangle
| hypersphere
| nifti
;
/* If the hyperrectangle is aligned with the axes, then two points are
* enough, if not we need all the points to be specified.
*/
hyperrectangle
: 'hyperrectangle' '{'
position ',' position
( ',' position ',' position )*
( ',' STRING )?
'}'
;
/* A hypersphere is defined by its center and a radius, independantly
* of the number of dimensions of the space. */
hypersphere
: 'hypersphere' '{'
position
',' positive_number
( ',' STRING )?
'}'
;
point
: 'point' '{' position ( ',' STRING )? '}'
;
/* Define a shape as the non-zero values in a NIfTI object, defined by
* nifti{
* lower_corner: position, // Optional, default to the origin
* rotation: [ position+ ], // Optional, no rotation by default
* bytes: uri(STRING), // uri to the NIfTI object
* spaceId: string
* }
*/
nifti
: 'nifti' '{'
(position ',' )?
( '[' position ( ',' position )* ']' ',' )?
byte_provider ','
STRING
'}'
;
/* TODO: STRING is assumed to be a well-formed URI, fully specify here?
*
* TODO: Add a provider for in-line raw-byte stream.
*/
byte_provider
: 'uri' '(' STRING ')'
;
/**********************************************************************/
/* POSITIONS */
/**********************************************************************/
/* Always returns a vector of numbers, a.k.a a position (a scalar will
* be represented as a vector of one element) */
position_expr
: str_cmp_icase
| str_cmp
| selector
| position
;
/* Compare lexicographically two strings, and returns a `position`:
* [-1] : String is lexicographically before,
* [ 0] : is equal,
* [ 1] : is after.
*/
str_cmp
: 'str_cmp' '(' selector ',' STRING ')'
;
/* Same, but case insensitive. */
str_cmp_icase
: 'str_cmp_ignore_case' '(' selector ',' STRING ')'
;
/* TODO: FIELDS are expected to be exisiting in the data model. Root Object is assumed to be the type of the ressource on which the POST call was done.
*/
selector
: ( FIELD )+
;
position
: '[' number ( ',' number )* ']'
;
/**********************************************************************/
/* TOKENS - STRINGS */
/**********************************************************************/
/* Accept field descriptor which
* 1. start with a dot ('.')
* 2. optionnally followed by a field name consisting of a letter or
* underscore, followed by letters, numbers or underscore,
* 3. optionnally followed by brakets enclosing an natural number
* denoting an offset in a list or array. */
FIELD
: '.' ( [a-zA-Z_] [a-zA-Z0-9_]* )? ('[' INTEGER ']')?
;
STRING
: '&quot;' (ESC | SAFECODEPOINT)* '&quot;'
;
fragment ESC
: '\\' ([&quot;\\/bfnrt] | UNICODE)
;
fragment UNICODE
: 'u' HEX HEX HEX HEX
;
fragment HEX
: [0-9a-fA-F]
;
fragment SAFECODEPOINT
: ~ [&quot;\\\u0000-\u001F]
;
/**********************************************************************/
/* TOKENS - NUMBERS */
/**********************************************************************/
/* We define 3 kinds of number, to avoid ambiguities in the rules. */
/* No optional leading '+' */
json_number
: '-'? NUM
;
positive_number
: '+'? NUM
;
number
: ( '+' | '-' )? NUM
;
NUM
: INTEGER ('.' [0-9]+ )? EXP?
;
fragment EXP
: [Ee] [+\-]? INTEGER
;
/* No leading zeros */
fragment INTEGER
: '0' | [1-9] [0-9]*
;
/**********************************************************************/
/* WHITESPACES &amp; COMMENTS */
/**********************************************************************/
COMMENTS
: ( '//' ~[\r\n]* | '/*' .*? '*/' ) -&gt; skip
;
WS
: [ \t\r\n]+ -&gt; skip
; // skip spaces, tabs, newlines
</code></pre>
<h1><a class="header" href="#query-grammar" id="query-grammar">Query Grammar</a></h1>
<p>You will find below the definition of this SDL, for queries. This builds on top of the <a href="filters.html">filters</a> grammar. </p>
<h2><a class="header" href="#queriesg4" id="queriesg4">queries.g4</a></h2>
<pre><code class="language-antlr">grammar queries;
import filters;
/**********************************************************************/
/* FORMATTING DATA */
/**********************************************************************/
queries
: projection_operators?
;
projection_operators
: nifti_operator
| json_operator
;
/* If selector is not provided, one (1) will be used as the values for
* each position where there is a point in bag_expression.
*
* If it is provided, it MUST resolve to a NUMBER. */
nifti_operator
: 'nifti' '(' ( selector ',' )? bag_expression ( ',' STRING )? ')'
;
json_operator
: 'json' '(' jslt ',' bag_expression ( ',' STRING )? ')'
;
jslt
: json
;
/**********************************************************************/
/* JSON */
/**********************************************************************/
/**
* Taken and adapted from:
* https://github.com/antlr/grammars-v4/blob/master/json/JSON.g4
*
* Some of the parser / lexer rules are in the imported grammar as well.
*/
json
: json_value
;
json_obj
: '{' json_pair (',' json_pair)* '}'
| '{' '}'
;
json_pair
: STRING ':' json_value
;
json_array
: '[' json_value (',' json_value)* ']'
| '[' ']'
;
json_value
: STRING
| json_number
| json_obj
| json_array
| 'true'
| 'false'
| 'null'
/* Add support to reference values from the selected bag. */
| selector
| aggregation_expr
;
/* The bag expression is implicit here, as this is te
* second argument to the json operator */
aggregation_expr
: 'count' '(' 'distinct'? selector ')'
| 'sum' '(' selector ')'
| 'min' '(' selector ')'
| 'max' '(' selector ')'
| 'nifti' '(' selector ')'
| 'mbb' '(' ')'
;
</code></pre>
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