Big Data Dictionary

Jaql

Jaql is a query language which is designed for Javascript Object Notation (JSON), a data format that has become popular because of its simplicity and modeling exibility. JSON is a simple, yet exible way to represent data that ranges from at, relational data to semi-structured, XML data. Jaql is primarily used to analyze large-scale semi-structured data. It is a functional, declarative query language which rewrites high-level queries when appropriate into a low-level query consisting of Hadoop jobs.

Core features include user extensibility and parallelism. Jaql consists of a scripting language and compiler, as well as a runtime component. It is able to process data with no schema or only with a partial schema. However, Jaql can also exploit rigid schema information when it is available, for both type checking and improved performance. Jaql uses a very simple data model, a JDM value is either an atom, an array or a record. Most common atomic types are supported, including strings, numbers, nulls and dates. Arrays and records are compound types that can be arbitrarily nested. In more detail, an array is an ordered collection of values and can be used to model data structures such as vectors, lists, sets or bags. A record is an unordered collection of name-value pairs and can model structs, dictionaries and maps. Despite its simplicity, JDM is very exible. It allows Jaql to operate with a variety of dierent data representations for both input and output, including delimited text les, JSON les, binary les, Hadoop's SequenceFiles, relational databases, key-value stores or XML documents. Functions are rst-class values in Jaql. They can be assigned to a variable and are high-order in that they can be passed as parameters or used as a return value. Functions are the key ingredient for reusability as any Jaql expression can be encapsulated in a function, and a function can be parameterized in powerful ways.