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A CQL extension for sortingMike Taylor <mike@indexdata.com>

Index Data – http://www.indexdata.com

A CQL extension for sorting Mike Taylor, Index Data <mike@indexdata.com>

Overview

Where we're headed:

The problem: sorting in SRU 1.1The solution: a CQL extension for sortingExamplesDescriptionThe sorting context setBNF grammarXCQL representationExplain (ZeeRex elements)

The problem: sorting in SRU 1.1

The sorting mechanism in SRU 1.1 is inadequate:

It requires its own parser.It uses XPath, a format- and schema-specific solution,It is incapable of expressing namespaces in the XPath.It requires its own parameter in the request.It is not extensible (e.g. Unicode sort) or profilable.It is tied directly to the SRU version.Sort criteria are not part of the query language,

(as is common in other query languages such as SQL.)

The solution: a CQL extension

The best solution is to add sorting support to the SRU'squery language, CQL:

Existing CQL indexes can be used in sort specifications (i.e. abstract access points).

Sorting indexes and their modifiers can be profiled in the same way as the core of CQL.

Only a single language parser is required in CQL, with minimal changes required to existing CQL parsers

Fringe benefit: applications of CQL other than SRU/W will benefit from the new capabilities.

An ounce of example is worth a ton of exposition

fish sortby title

fish sortby titlefish and frog sortby title

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.title

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.number

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.numberdc.title=fish sortby dc.title/sort.respectCase

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.numberdc.title=fish sortby dc.title/sort.respectCasedc.title=fish sortby dc.title/sort.respectCase/sort.descending

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.numberdc.title=fish sortby dc.title/sort.respectCasedc.title=fish sortby dc.title/sort.respectCase/sort.descendingdc.title=fish sortby dc.date dc.creator dc.title

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.numberdc.title=fish sortby dc.title/sort.respectCasedc.title=fish sortby dc.title/sort.respectCase/sort.descendingdc.title=fish sortby dc.date dc.creator dc.titledc.title=fish sortby dc.date/sort.missingOmit

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.numberdc.title=fish sortby dc.title/sort.respectCasedc.title=fish sortby dc.title/sort.respectCase/sort.descendingdc.title=fish sortby dc.date dc.creator dc.titledc.title=fish sortby dc.date/sort.missingOmitdc.title=fish sortby dc.date/sort.missingValue=1970

fish sortby titlefish and frog sortby titledc.title=fish sortby dc.titledc.title=fish sortby numberOfLegs/cql.numberdc.title=fish sortby dc.title/sort.respectCasedc.title=fish sortby dc.title/sort.respectCase/sort.descendingdc.title=fish sortby dc.date dc.creator dc.titledc.title=fish sortby dc.date/sort.missingOmitdc.title=fish sortby dc.date/sort.missingValue=1970>dc="http://deepcustard.org/1.0" fish sortby dc.custardDepth

Description of the sorting extension

Sort-specifications introduced by new "sortby" operator

"sortby" may only occur at the top level of a query

LHS of the "sortby" operator is a classic CQL query

RHS is an ordered list of sort keys, most significant first

Sort key is an index name, with optional modifiers

Indexes and modifiers may be from any context set

Unqualified indexes drawn from the prevailing context-set

Unqualified modifiers drawn from the CQL context set

(The concept of an index modifier is new with this proposal.)

The sorting context-set

No indexes, relations, etc. Only index modifiers.

ignoreCase – case-insensitive (usually default)

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sorting

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sortingignoreAccents / respectAccents

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sortingignoreAccents / respectAccentsascending – sort in ascending order (usually default)

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sortingignoreAccents / respectAccentsascending – sort in ascending order (usually default)descending – sort in descending order

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sortingignoreAccents / respectAccentsascending – sort in ascending order (usually default)descending – sort in descending ordermissingOmit / missingFail / missingLow / missingHigh

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sortingignoreAccents / respectAccentsascending – sort in ascending order (usually default)descending – sort in descending ordermissingOmit / missingFail / missingLow / missingHighmissingValue=val – how to sort records lacking key data

ignoreCase – case-insensitive (usually default)respectCase – case-sensitive sortingignoreAccents / respectAccentsascending – sort in ascending order (usually default)descending – sort in descending ordermissingOmit / missingFail / missingLow / missingHighmissingValue=val – how to sort records lacking key datalocale=val – locale-specific sorting rules (accents, etc.)

cqlQuery ::=

prefixAssignment cq

lQuery | scopedClaus

e [sortSpec]

prefixAssignment ::=

'>' prefix '=' uri

| '>' uri

scopedClause ::=

scopedClause boolea

nGroup searchClause

| searchClause

booleanGroup ::=

boolean [modifierLi

boolean ::=

'and' | 'or' | 'not

' | 'prox'

searchClause ::=

'(' cqlQuery ')'

index relation sear

chTerm

searchTerm

relation ::=

comparitor [modifie

rList]

comparitor ::=

comparitorSymbol |

namedComparitor

comparitorSymbol ::=

'=' | '>' | '<' | '

>=' | '<=' | '<>'

namedComparitor ::=

identifier

modifierList ::=

modifierList modifi

er | modifier

modifier ::=

'/' modifierName [c

omparitorSymbol modi

fierValue]

prefix ::=

uri ::=

modifierName ::=

modifierValue ::=

searchTerm ::=

index ::=

term ::=

identifier | 'and'

| 'or' | 'not' | 'pr

ox' | 'sortby'

identifier ::=

charString1 | charS

tring2

sortSpec ::=

sortSpec singleSpec

| singleSpec

singleSpec ::=

index [modifierList

Zzzzzzz ...

You can switch off now if you like.

The rest is boringly technical.

BNF grammar

Two existing rules need to change:

cqlQuery ::= prefixAssignment cqlQuery | scopedClause [sortSpec]term ::= identifier | 'and' | 'or' | 'not' | 'prox' | 'sortby'

And two new rules are needed:

sortSpec ::= sortSpec singleSpec | singleSpecsingleSpec ::= index [modifierList]

XCQL representation<sortKeys>

<key><index>dc.creator</index><modifiers>

<modifier><name>sort.missingValue</name><value>frog</value>

</modifier><modifier>

<name>sort.descending</name></modifier>

</modifiers></key>

</sortKeys>

Explain (ZeeRex elements)<indexInfo> <set name="sort" identifier="http://zing.z3950.org/cql/sorting/1.0"/> <index sort="true"> <title>Dublin Core Creator (Author)</title> <map><name set="dc">creator</name></map> </index></indexInfo><configInfo> <setting type="maximumSortKeys">3</setting> <default type="sortCase">respectCase</default> <default type="sortDirection">descending</default> <default type=”missingFail”/></configInfo>