Jaql

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.

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 ;

Source:^[5]

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

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"
  }
]

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

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.

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

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.

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

• jq
• JSONiq
• XPath
• XQuery

• Definition of the JAQL language
• JAQL in Hadoop – A Brief Introduction
• Comparison against HIVE and PIG Archived 2014-03-01 at the Wayback Machine
• Adaptive Processing of User-Defined Aggregates in Jaql