Jaql
Jaql (JAQL) is a functional data processing and query language most commonly used for JSON query processing on BigData.
It started as an Open Source project at Google[1] but the latest release was on 7/12/2010. 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 linkbreaked after the arrow, this is also a common technique in Twitter SCALDING:
source -> operator1(parameter)
-> operator2(parameter)
-> operator2(parameter)
-> operator3(parameter)
-> operator4(parameter)
-> sink ;
Core Operators[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, mgr: false},
{name: "Vince Wayne", income: 32500, mgr: false},
{name: "Jane Dean", income: 72000, mgr: true},
{name: "Alex Smith", income: 25000, mgr: false}
];
data -> filter $.mgr;
[
{
"income": 72000,
"mgr": true,
"name": "Jane Dean"
}
]
data -> filter $.income < 30000;
[
{
"income": 20000,
"mgr": false,
"name": "Jon Doe"
},
{
"income": 2500,
"mgr": 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.
References
External links
- Definition of the JAQL language
- JAQL Introduction
- Comparison against HIVE and PIG
- Adaptive Processing of User-Defined Aggregates in Jaql