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- Forward
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- Features - -
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- What's new
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- Documentation - - -
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- Implementation
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- The authors
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- Links
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What's new
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- This page reports the newly implemented
- features of MathQL-1 that are not included in the official documentation yet.-
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- MathQL-1 version 4 now under development ...
-We are now implementing the new unstable version of MathQL-1 (i.e. MathQL-1.4).
-The main goals of this release are:-
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- A clear distinction between the core language and the auxiliary
-functions, which should be part of an extensible library.
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- The elimination of the explicit casts between the <query>
-and <value> types in queries.
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- A tight connection with a query generator (i.e HELM query generator).
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- Changes and additions to MathQL-1 operators:
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- The add operator now accepts a syntax extension allowing - to specify more than one explicit attribute group. - -
The syntax now is:- -
<query> := "add" [ "distr" ]? [ <groups> | -<avar> ] "in" <query>- -
- <groups> := <group> [ ";" <group> ]*
- <group> := <attribute> [ "," <attribute> ]*
- <attribute> := <value> "as" <path>
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- Examples:
- the query add "1" as "a", "2" as "b" in subj "A" gives the result - "A" attr {"a"="1"; "b"="2"} while
- the query add "1" as "a"; "2" as "b" in subj "A" gives the result - "A" attr {"a"="1"}, {"b"="2"}.
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- The new align operator takes an integer i (represented - as a string), a multiple string value v and returns the same v - where each string with length n < i is prefixed with i - n - spaces. The syntax of the add operator is: - -
<value> := "align" <string> "in" <value>- -
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- This operators aligns strings containing numbers so that their alphabetic - order agrees with their numeric order.
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- The intersect operator now intersects the attribute - groups of the matching subject strings set-theoretically rather than making - their "Cartesian product". This semantics reduces the computational costs - and makes intersection the dual of union. - -
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- The property operator now accepts more than one isfalse - clause to increase the complexity of the constraint condition used to filter - the raw query results. This feature is exploited in the queries produced - by the HELM query generator. - -
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- The PostgreSQL database map is a file describing how the MathQL-1
- interpreter must interact with the underlying PostgreSQL database, when
-it is run in Postgres mode. Currently this file contains the following information:The PostgreSQL database map:
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- the database connection string to be used when the interpreter - opens a connection with the database; - -
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- the map describing the correspondence between the metadata - access paths used by the property operator and the fields of the -database tables. - -
- The first line must contain the database connection string and the subsequent - lines contain the map with the following syntax:
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- blank lines: ignored (used for separation); - -
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- lines starting with a # followed by a space: ignored (used
-for comments);
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- <table_name> <field_name> "<-"
- [ <path_component> ]*
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the information about the metadata denoted by the given - path is found in the given field of the given table in the database. For -example the line:- -
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- refobj h_occurrence <- refObj h:occurrence
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- tells that the metadata denoted by the path /"refObj"/"h:occurrence" - is found in the field "h_occurrence" of the table "refobj" in the database, - while:
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- refobj source <-
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- tells that the metadata denoted by the path / is found in the field - "source" of the table "refobj" in the database;
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- <table_name> <field_name> "<+"
- [ <path_component> ]*
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same as the previous but defines a default table and field - for the given path. This is used to force the interpreter to query a particular - table when the information denoted by a path can be found in more than one - table and field. For example:- -
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- objectname source <+
- refobj source <-
- refrel source -<-
- refsort source <-
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- tells that the metadata denoted by the path / is found in the "source" - field of the "objectname", "refobj", "refrel" and "refsort" tables, and -that the first choice is preferred;
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- <table_name> "<-" [ <path_component> ]* - -
the given path denotes a structured metadata whose components - are found in the fields of the given table. For example:- -
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- refobj <- refObj
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- tells that the path /"refObj" denotes a structured metadata whose - components are found in the fields of the table "refobj";
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- <table_name> "<+" [ <path_component> ]* - -
same as the previous but tells that this is a default correspondence; -- -
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- <virtual_table_name> "->" <concrete_table_name> - -
defines a correspondence between a virtual table name an - a concrete table name. All the <table_name> entries represent virtual - table names that are mapped to concrete table names using the identity function - unless a particular mapping is defined for them using the above construction. - This mechanism allows to define several set of metadata on the same database - table as in:- -
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- refobj source - <-
- refobj h_occurrence <- - refObj h:occurrence
- backpointer source - <- backPointer h:occurrence
- backpointer h_occurrence <-
- backpointer - -> refobj
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which defines four path accessing two virtual tables ("refobj" - and "backpointer") and then maps these tables in a single concrete table;- -
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- "->"
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a line like this must end the map file.- Here you can find the current - version of PostgreSQL database map for HELM.
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- How does the interpreter use the map? The map file is read -during the interpreter initialization process from the file pointed by the -MATHQL_DB_MAP environment variable and is used during the execution of each - property operation in the issued queries.When executing a property -operation, the interpreter uses the map to find the smallest set of database -tables containing the information required by the given access paths and then -queries these tables to obtain the wanted information.
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