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CQL – a Common Query Language

Learn about CQL, a versatile query language for easy and complex queries. Explore motivation, examples, and application in various contexts. Discover key concepts like booleans, pattern matching, indexes, and more. 8 Relevant

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CQL – a Common Query Language

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  1. CQL – a Common Query Language What CQL is Motivation Examples and explanation Applications Implementation CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  2. Chapter 1: What CQL is • CQL is a query language: – For humans to type – For query forms to generate – For translating other languages into • The only query language of SRW/SRU • Also applicable in other contexts: – Z39.50 (instead of the Type-1 Query) – Query boxes for web searches CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  3. Chapter 2: Motivation Most query languages fall into one of two camps: • Complex and powerful, but cryptic and hard to learn – SQL, Prefix Query Format (PQF), XML Query • Easy to learn and use, but lacking in power – Google, AltaVista, CCL CQL aims to “make simple queries easy, and complex queries possible” (to paraphrase Larry Wall, of Perl) CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  4. Learning curves for query languages SQL Effort in learning query language Power of query that can be expressed CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  5. Learning curves for query languages SQL Effort in learning query language Google Power of query that can be expressed CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  6. Learning curves for query languages SQL CQL Effort in learning query language Google Power of query that can be expressed CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  7. Important concepts • Simple terms • Quoting • Booleans • Parentheses • Pattern matching • Word anchoring • Indexes • Prefixes • Context sets • Relations Esoteric concepts • Proximity • Relation modifiers • Boolean modifiers • Prefix mapping Chapter 3: Examples and explanation CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  8. CQL features: simple terms Here are some perfectly good CQL queries: • fish • Churchill • dinosaur • comp.sources.misc CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  9. CQL features: quoting Double-quote marks remove the special meanings of special characters like space (which otherwise separates tokens) and of keywords such as “and” and “or”. • "dinosaur" • "the complete dinosaur" • "ext–>u.generic" • "and" • "the \"nuxi\" problem" (Backslash removes the special meaning of following double-quote characters.) CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  10. CQL features: booleans The keywords “and” and “or” are boolean operators. The keyword “not” is an and-not binary operator. There is no unary negation operator. Case is not significant, so “AND” and “aNd” also work. • dinosaur or bird • dinosaur not reptile • dinosaur and bird and reptile • dinosaur and bird or dinobird • dinosaur not theropod not ornithischian CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  11. CQL features: boolean precedence The “and”, “or” and “not” booleans all have equal precedence and are evaluated left-to-right. • dinosaur and bird or dinobird MEANS (dinosaur and bird) or dinobird • dinosaur or bird and dinobird MEANS (dinosaur or bird) and dinobird NOT dinosaur or (bird and dinobird) CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  12. CQL features: parentheses Parentheses may be used to override the default left-to-right parsing of boolean operators. • dinosaur and (bird or dinobird) • dinosaur or (bird and dinobird) • (bird or dinosaur) and (feathers or scales) • "feathered dinosaur" and (yixian or jehol) • (((a and b) or (c not d) not (e or f and g)) and h not i) or j CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  13. CQL features: pattern matching There are two pattern-matching characters: * matches any number of characters ? matches any single character A preceding backslash removes their special meaning. • dinosaur* – matches “dinosaurs”, “dinosauria” • *sauria – matches “dinosauria”, “carnosauria” • man?raptor – matches “maniraptor”, “manuraptor” • man?raptor* – matches the plurals of these • "the comp*saur" – matches “the complete dinosaur” • char\* – matches literal “char*” CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  14. CQL features: word anchoring A word beginning with “^” must occur at the start of its field. A word ending with “^” must occur at the end of its field. • dinosaur – matches “the complete dinosaur” • dinosaur^ – also matches • ^dinosaur – does not match • the – matches “the complete dinosaur” • ^the – also matches • the^ – does not match CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  15. CQL features: indexes A term of the form name=value is a query for the specified value occurring within the named index. • title=Churchill – finds biographies of Churchill • author=Churchill – finds books written by him • title=dinosaur and author=farlow • title=(dinosaur and bird) • subject=(dinosaur* or pterosaur*) Index names are case-insensitive, so “title” is the same index as “TITLE”, “Title” or “tiTLe”. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  16. CQL features: prefixes The meaning of an index can be specified more fully by a prefix indicating what context set it is from. The meaning of “title” is different in cross-domain searching (Dublin Core), bibliographic searching (Bath Profile) and heraldry. • dc.title="the complete dinosaur" • property.title=freehold • heraldry.title=(viscount or duke) • cql.serverChoice=fruit • cql.resultSet=YXJjaGJpc2hvcAp Prefixes are case-insensitive. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  17. CQL features: context sets A context set is a set of indexes that are related to a particular area (plus some other more esoteric stuff that you can ignore). For example, the Dublin Core context set contains indexes for searching against the fifteen DC elements: title, creator, subject, description, publisher, contributor, date, type, format, identifier, source, language, relation, coverage, rights. The context set prose must define their semantics. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  18. CQL features: some context sets A few core sets created by the SRW editorial board: • CQL – for core indexes such as resultSet • DC – for metadata searching with Dublin Core • Rec – metadata about the record, not the resource • Net – network concepts such as hostname and port Also, many application-specific sets: • Bath, Zthes, CCG, Music • Rel – deep voodoo for relevance matching • GILS is in development Where do context sets come from? • You can just make them up! No-one can stop you! CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  19. A digression on the CQL context set The CQL context set is special. It contains some “magic” indexes: • cql.anywhere – searches in all the indexes available • cql.serverChoice – allows the server to choose whatever index or indexes are suitable • cql.resultSetId – finds the records obtained in a previous search, e.g. for refinement by combining with other query terms. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  20. CQL features: relations Usually “=” connects an index with its relation, but all the other obvious numeric relations are supported: • Height = 13 • numberOfWheels <= 3 • numberOfPlates = 18 • lengthOfFemur > 2.4 • BioMass >= 100 • NumberOfToes <> 3 (inequality) CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  21. CQL features: special relations The keywords “any” and “all” can be used as relations, indicating that any one of, or all of, the words specified in the term must be found in the index: • author all "kernighan ritchie" – shorthand for author=kernighan and author=ritchie • author any "kernighan ritchie thompson" – shorthand for author=kernighan or author=ritchie or author=thompson CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  22. CQL features: esoterica “You are not expected to understand this.” – comment in the Unix Version 7 source code. The point is that new users are not required to understand this, and may happily use CQL for many years – perhaps forever – without needing to. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  23. CQL esoterica: proximity The “prox” boolean, by default, requires its operands to be next to each other, in either order: • cervical prox vertebra – equivalent to "cervical vertebra" or "vertebra cervical" • (cervical or dorsal) prox vertebra – equivalent to "cervical vertebra" or "dorsal vertebra" or "vertebra cervical" or "vertebra dorsal" CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  24. CQL esoterica: proximity II Modifiers can generalise the semantics of proximity: • cervical prox/distance<=5/ vertebrae – within five words of each other • cervical prox/distance=0/unit=sentence vertebrae – within the same sentence • cervical prox/distance>0/unit=paragraph vertebrae – in different paragraphs • cervical prox/ordered vertebrae – in the specified order: exactly equivalent to "cervical vertebra" CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  25. CQL esoterica: relation modifiers Modifiers can refine the semantics of relations: • title =/stem dig – finds “dig”, “digging”, “dug”, etc. • title any/relevant "dinosaur bird reptile" – finds “sauropods”, “avian”, “crocodile”, “snake”, etc. • author =/fuzzy tailor – finds “Mike Taylor” • phoneNumber exact/fuzzy "020 8348 6768" – finds “020 8348 6769” CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  26. CQL esoterica: relation modifiers II Relation modifiers can be overloaded to specify extra information about the term that the relation joins to the index: • createdDate >/isoDate "2004-03-12 09:45:00" – the term is in ISO 8601 format. • Location within/geom.polygon "(12,46) (15,52)" – the term indicates a polygon of two points (i.e. a straight line) rather than the corners of a rectangle. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  27. CQL esoterica: boolean modifiers Modifiers can refine the semantics of boolean operators. We've already seen some examples of this in proximity. • cervical prox/distance<=5/ vertebrae – within five words of each other • cervical or/exclusive vertebrae – one or the other, but not both. • "denenberg or/rel.mean "information retrieval" • "denenberg or/rel.sum "information retrieval" • "denenberg or/rel.max "information retrieval" – average, total or maximum relevance of operands CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  28. CQL esoterica: prefix mapping So far, we have been free and easy with index prefixes such as “dc”. But how do we know what they mean? Why should “dc” mean Dublin Core rather than Deep Custard? • dc.custardDepth <= 20 Why should “bath” mean the Bath Profile for bibliographic searching instead of plumbing supplies? • bath.capacityInGallons > 45 CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  29. CQL esoterica: prefix mapping II Prefixes are just convenient, easy-to-type abbreviations. The real identifier of a context set is its URI. For example, the Dublin Core context set is info:srw/cql-context-set/1/dc-v1.1 but we map that URI to a prefix for convenience. This is exactly like XML namespaces: they are identified by URIs, but the URIs do not appear in the names of elements or attributes: short prefixes are used instead. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  30. CQL esoterica: prefix mapping III In XML, a prefix is associated with a namespace using: • <element xmlns:prefix="http://example.org/xyz/"> In CQL, a prefix is associated with a namespace using: • >prefix=http://example.org/xyz/ and the rest of the query follows. The following queries are exactly equivalent: • >dc=info:srw/cql-context-set/1/dc-v1.1 dc.title=fish • >yx=info:srw/cql-context-set/1/dc-v1.1 yx.title=fish Most applications will have established default mappings. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  31. CQL esoterica: prefix mapping IV It is possible to establish the context set from which indexes with no explicit prefix are taken by omitting the “prefix=” part from the mapping: • >http://example.org/heraldry/ title=baron and side=sinister So the following queries are exactly equivalent: • >info:srw/cql-context-set/1/dc-v1.1 title=fish • >yx=info:srw/cql-context-set/1/dc-v1.1 yx.title=fish CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  32. CQL esoterica: prefix mapping V Finally ... Finally! :-) Prefix mappings can be stacked up: • >dc = info:srw/cql-context-set/1/dc-v1.1 >bath=http://zing.z3950.org/cql/bath/2.0/ >rec=info:srw/cql-context-set/2/rec-1.0 rec.created < 2004-10-09 and dc.title=ecology and bath.conferenceName=dinosaur (Yes, this is all one query.) CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  33. CQL esoterica: prefix mapping VI Don't try this at home. CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  34. Chapter 4: Applications CQL has been deployed in many kinds of application: • Google-like structureless searching • Simple metadata searching with the Dublin Core • Bath Profile for bibliographic data • Zthes profile for hierarchical thesaurus navigation • CCG for collectable card games • Music – musicalKey, arranger, duration, etc. • GILS (Global Information Locator Service) • ... your application goes here! CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  35. Chapter 5: Implementations There are good-quality free CQL implementations in several important languages: • Java (Mike Taylor's CQL-Java package) • C/C++ (Adam Dickmeiss in Index Data's YAZ) • Python (Rob Sanderson in Cheshire) • Perl (Ed Summers' CQL::Parser module) • Visual Basic is in development (Thomas Habing) • ... your language goes here! CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  36. Conclusion: What to take home • CQL makes easy queries easy and hard ones possible • You can use it well without learning the hard bits • It is used in SRW/SRU but also applicable elsewhere • It is extensible through context sets • Existing context sets support lots of applications • There are free implementations in several languages • Tutorial on-line at: http://zing.z3950.org/cql/intro.html CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

  37. CQL esoterica: relation modifiers II Relation modifiers can be used to define essentially new relations. Some hypothetical examples: • location </geom.within "(12,46) (15,52)" – points within the specified rectangle • task >/proj.prerequisite uiDesign – tasks that must be performed before the design of the user interface • location =/geography.sameState "Las Vegas" – places in the same state as Las Vegas CQL – a Common Query Language Mike Taylor <mike@indexdata.com>

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