Query language (QL) refers to any computer programming language that
requests and retrieves data from database and information systems by sending queries.
It works on user entered structured and formal programming command based
queries to find and extract data from host databases.
requests and retrieves data from database and information systems by sending queries.
It works on user entered structured and formal programming command based
queries to find and extract data from host databases.
Query language may also be termed database query language. Query language
is primarily created for creating, accessing and modifying data in and out from
a database management system (DBMS)
is primarily created for creating, accessing and modifying data in and out from
a database management system (DBMS)
Examples of query language
· QL is a proprietary
object-oriented query language for querying relational databases;
successor of Datalog;
object-oriented query language for querying relational databases;
successor of Datalog;
· Contextual Query Language (CQL) a formal
language for representing queries to information retrieval systems such as web
indexes or bibliographic catalogues.
language for representing queries to information retrieval systems such as web
indexes or bibliographic catalogues.
· Concept-Oriented Query Language (COQL) is used in the
concept-oriented model (COM). It is based on a novel data
modeling construct, concept, and uses such operations as projection and
de-projection for multi-dimensional analysis, analytical operations and
inference;
concept-oriented model (COM). It is based on a novel data
modeling construct, concept, and uses such operations as projection and
de-projection for multi-dimensional analysis, analytical operations and
inference;
· FQL enables you to use
a SQL-style interface to query
the data exposed by the Graph API. It provides advanced features not available in the Graph API.
a SQL-style interface to query
the data exposed by the Graph API. It provides advanced features not available in the Graph API.
· PQL is a special-purpose programming
language for managing process models based on information about scenarios that these models describe.
language for managing process models based on information about scenarios that these models describe.
Functions and capacity of a query language
Value
manipulation
The following functions
operate on normal attribute values.
operate on normal attribute values.
Bin (value, bins)
Separates numeric values into 'bins', based on a list of values providing the bin boundaries
Duration (start_time,
end_time)
Calculates the amount of
time elapsed between the two dates and returns the result as a string of the
form ‘days.hours:minutes:seconds‘.
time elapsed between the two dates and returns the result as a string of the
form ‘days.hours:minutes:seconds‘.
Default Number (value,
default_value)
Attempts to convert the
value into a number and if it is not possible returns the default value.
value into a number and if it is not possible returns the default value.
Format UTC Time (time_value,
format)
Identical to formatTime,
except that it does not perform timezone conversion.
except that it does not perform timezone conversion.
Friendly Time (time_value)
Converts the internal
time format into a human readable string, taking into account time zones and
daylight saving times, based on the time zone of the appliance.
time format into a human readable string, taking into account time zones and
daylight saving times, based on the time zone of the appliance.
Destroyed (node)
Returns True if the node has been destroyed, False if not. Returns [invalid
node] if the argument is not a node. Works on lists of nodes
as well, returning a list of boolean values
node] if the argument is not a node. Works on lists of nodes
as well, returning a list of boolean values
Specialist history functions
The following history
functions can be used for specialist purposes:
functions can be used for specialist purposes:
New In Attr (node, attr,
timeA, timeB)
Retrieves the node’s
specified attribute at the two times. The attribute is expected to contain a
list. Returns a list containing all items that were present in the list
at timeB that were not present at timeA.
specified attribute at the two times. The attribute is expected to contain a
list. Returns a list containing all items that were present in the list
at timeB that were not present at timeA.
Attr Spread (node, attr,
timeA, timeB)
Returns a list containing
all unique values that the attribute has had between the two times.
all unique values that the attribute has had between the two times.
New In Attr Spread(node,
attr, timeA, timeB, timeC)
A cross between newInAttr
and attrSpread. Returns a list of values for the attribute that existed at any
time between timeB and timeC,
but which did not exist at any time between timeA and timeB.
and attrSpread. Returns a list of values for the attribute that existed at any
time between timeB and timeC,
but which did not exist at any time between timeA and timeB.
History Subset
Reports on a subset of the node history between the two times. attrs is
a list of attribute names to report; rels is a list of colon-separated
relationship specifications to report.
a list of attribute names to report; rels is a list of colon-separated
relationship specifications to report.
