Expression language: Difference between revisions

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{{Short description|Computer language for creating a machine readable representation of ___domain knowledge}}

{{Merge|Unified Expression Language|date=October 2009}}

{{unsourced|date=February 2024}}

An '''expression language''' is a [[computer language]] for creating a [[machine readable]] representation of specific [[___domain knowledge]]. Examples include:

'''Expression Language''' (EL) is a scripting language which allows access to [[Java (Sun)|Java]] components ([[JavaBean]]s) through [[JavaServer Pages|JSP]]. Since [[JavaServer Pages#JSP 2.0|JSP 2.0]], it has been used inside [[JavaServer Pages|JSP]] tags to separate Java code from JSP, and to allow easier access to Java components (than in Java code).

*[[Advanced Boolean Expression Language]], an obsolete hardware description language for hardware descriptions

Evolution of EL occurred to make scripting easier for web-content designers who have little or practically no knowledge of the core Java Language. This scripting language makes JSP a scripting language in the true sense. Before EL, JSP consisted of some special tags like [[scriptlet]]s, expressions etc. within which Java code was written explicitly. With EL the web-content designer needs only to know how to make proper calls to core Java methods and can enjoy the true scripting flavour of a scripting language.

*[[Data Analysis Expressions]] (DAX), an expression language developed by Microsoft and used in Power Pivot, among other places

*[[Jakarta Expression Language]], a ___domain-specific language used in Jakarta EE web applications. Formerly known as "Unified Expression Language", "Expression Language" or just "the Expression Language").

*[[Rights Expression Language]]s, machine processable language used for representing immaterial rights such as copyright and license information

{{compucomp-langsci-stub}}

EL is, both syntactically and semantically, similar to [[JavaScript]] expressions:

* there is no typecasting

* type conversions are usually done implicitly

* double and single quotes are equivalent

* <code>object.property</code> has the same meaning as <code>object['property']</code>

[[Category:ScriptingComputer languages]]

EL also liberates the programmer from having to know the particularities of how the values are actually accessed: <code>object.property</code> can mean (depending on what the <code>object</code> is) either <code>object.get("property")</code> or <code>object.getProperty("property")</code> or <code>object.getProperty()</code> etc.

==See also==

* [[OGNL]]- An open source expression language used by [[WebWork]] (and [[Struts]]2).

* [[MVEL]]- Another open source EL used in many Java-based projects.

==External links==

* [http://java.sun.com/j2ee/1.4/docs/tutorial/doc/JSPIntro7.html Java- Expression Language]

[[Category:Scripting languages]]

{{compu-lang-stub}}

[[fr:Expression Language]]

[[hu:Expression Language]]

[[pt:Linguagem de Expressão]]

[[ru:Expression Language]]