Jaql

Jaql

Paradigm	Functional
Designed by	Vuk Ercegovac (Google)
First appeared	October 9, 2008;16 years ago (2008-10-09)
Stable release	0.5.1 / July 12, 2010;14 years ago (2010-07-12)
Implementation language	Java
OS	Cross-platform
License	Apache License 2.0
Website	code.google.com/p/jaql/m
Major implementations
IBM BigInsights

Jaql (pronounced "jackal") is a functional data processing and query language most commonly used for JSON query processing on big data.

It started as an open source project at Google ^[1] but the latest release was on 2010-07-12. IBM ^[2] took it over as primary data processing language for their Hadoop software package BigInsights.

Although having been developed for JSON it supports a variety of other data sources like CSV, TSV, XML.

A comparison ^[3] to other BigData query languages like PIG Latin and Hive QL illustrates performance and usability aspects of these technologies.

Jaql supports ^[4] lazy evaluation, so expressions are only materialized when needed.

Syntax

The basic concept of Jaql is

source->operator(parameter)->sink;

where a sink can be a source for a downstream operator. So typically a Jaql program has to following structure, expressing a data processing graph:

source->operator1(parameter)->operator2(parameter)->operator2(parameter)->operator3(parameter)->operator4(parameter)->sink;

Most commonly for readability reasons Jaql programs are linebreaked after the arrow, as is also a common idiom in Twitter Scalding:

source->operator1(parameter)->operator2(parameter)->operator2(parameter)->operator3(parameter)->operator4(parameter)->sink;

Core operators

Source: ^[5]

Expand

Use the EXPAND expression to flatten nested arrays. This expression takes as input an array of nested arrays [ [ T ] ] and produces an output array [ T ], by promoting the elements of each nested array to the top-level output array.

Filter

Use the FILTER operator to filter away elements from the specified input array. This operator takes as input an array of elements of type T and outputs an array of the same type, retaining those elements for which a predicate evaluates to true. It is the Jaql equivalent of the SQL WHERE clause. Example:

data=[{name:"Jon Doe",income:20000,manager:false},{name:"Vince Wayne",income:32500,manager:false},{name:"Jane Dean",income:72000,manager:true},{name:"Alex Smith",income:25000,manager:false}];data->filter$.manager;[{"income":72000,"manager":true,"name":"Jane Dean"}]data->filter$.income<30000;[{"income":20000,"manager":false,"name":"Jon Doe"},{"income":25000,"manager":false,"name":"Alex Smith"}]

Group

Use the GROUP expression to group one or more input arrays on a grouping key and applies an aggregate function per group.

Join

Use the JOIN operator to express a join between two or more input arrays. This operator supports multiple types of joins, including natural, left-outer, right-outer, and outer joins.

Sort

Use the SORT operator to sort an input by one or more fields.

Top

The TOP expression selects the first k elements of its input. If a comparator is provided, the output is semantically equivalent to sorting the input, then selecting the first k elements.

Transform

Use the TRANSFORM operator to realize a projection or to apply a function to all items of an output.

See also

• jq
• JSONiq
• XPath
• XQuery

References

1. Original Jaql project
2. Initial Publication
3. Stewart, Robert J.; Trinder, Phil W.; Loidl, Hans-Wolfgang (2011). "Comparing High Level MapReduce Query Languages". Advanced Parallel Processing Technologies. Lecture Notes in Computer Science. Vol. 6965. pp. 58–72. doi:10.1007/978-3-642-24151-2_5. ISBN   978-3-642-24150-5.
4. JAQL in Hadoop, a brief introduction
5. IBM BigInsights Documentation

External links

• Definition of the JAQL language
• JAQL Introduction
• Comparison against HIVE and PIG
• Adaptive Processing of User-Defined Aggregates in Jaql