# ECL (data-centric programming language)

ECL (Enterprise Control Language) is a declarative, data-centric programming language designed in 2000 to allow a team of programmers to process big data across a high performance computing cluster without the programmer being involved in many of the lower level, imperative decisions.

## History

ECL was initially designed and developed in 2000 by David Bayliss as an in-house productivity tool within Seisint Inc and was considered to be a ‘secret weapon’ that allowed Seisint to gain market share in its data business. Equifax had an SQL-based process for predicting who would go bankrupt in the next 30 days, but it took 26 days to run the data. The first ECL implementation solved the same problem in 6 minutes. The technology was cited as a driving force behind the acquisition of Seisint by LexisNexis and then again as a major source of synergies when LexisNexis acquired ChoicePoint Inc.

## Language constructs

ECL, at least in its purest form, is a declarative, data-centric language. Programs, in the strictest sense, do not exist. Rather an ECL application will specify a number of core datasets (or data values) and then the operations which are to be performed on those values.

### Hello world

ECL is to have succinct solutions to problems and sensible defaults. The "Hello World" program is characteristically short:
Perhaps a more flavorful example would take a list of strings, sort them into order, and then return that as a result instead.
The statements containing a := are defined in ECL as attribute definitions. They do not denote an action; rather a definition of a term. Thus, logically, an ECL program can be read: "bottom to top"
What is an SD?
SD is a D that has been sorted by ‘Value’
What is a D?
D is a dataset with one column labeled ‘Value’ and containing the following list of data.

### ECL primitives

ECL primitives that act upon datasets include SORT, ROLLUP, DEDUP, ITERATE, PROJECT, JOIN, NORMALIZE, DENORMALIZE, PARSE, CHOSEN, ENTH, TOPN, DISTRIBUTE

### ECL encapsulation

Whilst ECL is terse and LexisNexis claims that 1 line of ECL is roughly equivalent to 120 lines of C++, it still has significant support for large scale programming including data encapsulation and code re-use. The constructs available include MODULE, FUNCTION, FUNCTIONMACRO, INTERFACE, MACRO, EXPORT, SHARED

### Support for Parallelism in ECL

In the HPCC implementation, by default, most ECL constructs will execute in parallel across the hardware being used. Many of the primitives also have a LOCAL option to specify that the operation is to occur locally on each node.

### Comparison to Map-Reduce

The Hadoop Map-Reduce paradigm consists of three phases which correlate to ECL primitives as follows.
| Hadoop Name/Term | ECL equivalent | Comments |
| MAPing within the MAPper | PROJECT/TRANSFORM | Takes a record and converts to a different format; in the Hadoop case the conversion is into a key-value pair |
| SHUFFLE (Phase 1) | DISTRIBUTE(,HASH(KeyValue)) | The records from the mapper are distributed depending upon the KEY value |
| SHUFFLE (Phase 2) | SORT(,LOCAL) | The records arriving at a particular reducer are sorted into KEY order |
| REDUCE | ROLLUP(,Key,LOCAL) | The records for a particular KEY value are now combined |