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ECL Basics

Overview

Enterprise Control Language (ECL) has been designed specifically for huge data projects using the LexisNexis High Performance Computer Cluster (HPCC). ECL's extreme scalability comes from a design that allows you to leverage every query you create for re-use in subsequent queries as needed. To do this, ECL takes a Dictionary approach to building queries wherein each ECL definition defines an expression. Each previous Definition can then be used in succeeding ECL definitions--the language extends itself as you use it.

Definitions versus Actions

Functionally, there are two types of ECL code: Definitions (AKA Attribute definitions) and executable Actions. Actions are not valid for use in expressions because they do not return values. Most ECL code is composed of definitions.

Definitions only define what is to be done, they do not actually execute. This means that the ECL programmer should think in terms of writing code that specifies what to do rather than how to do it. This is an important concept in that, the programmer is telling the supercomputer what needs to happen and not directing how it must be accomplished. This frees the super-computer to optimize the actual execution in any way it needs to produce the desired result.

A second consideration is: the order that Definitions appear in source code does not define their execution order--ECL is a non-procedural language. When an Action (such as OUTPUT) executes, all the Definitions it needs to use (drilling down to the lowest level Definitions upon which others are built) are compiled and optimized--in other words, unlike other programming languages, there is no inherent execution order implicit in the order that definitions appear in source code (although there is a necessary order for compilation to occur without error--forward references are not allowed). This concept of "orderless execution" requires a different mindset from standard, order-dependent programming languages because it makes the code appear to execute "all at once."

Syntax Issues

ECL is not case-sensitive. White space is ignored, allowing formatting for readability as needed.

Comments in ECL code are supported. Block comments must be delimited with /* and */.

/* this is a block comment - the terminator can be on the same line
or any succeeding line -- everything in between is ignored */

Single-line comments must begin with //.

// this is a one-line comment

ECL uses the standard object.property syntax used by many other programming languages (however, ECL is not an object-oriented language) to qualify Definition scope and disambiguate field references within tables:

ModuleName.Definition //reference an definition from another module/folder
Dataset.Field       //reference a field in a dataset or recordset