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Matters of syntax: ConciseXML builds upon the important qualities of XML and S-Expressions.

Article Excerpt
ConciseXML is a new syntax I co-developed with Christopher Fry that builds on the best features of XML and S-Expressions while eliminating their constraints.

XML originated with the document-markup world of SGML and has become the leading syntax of the Internet. Its use been for documents and data--not for programming logic.

S-Expressions, or symbolic expressions, is the syntax behind Lisp-like languages, including Scheme. Basically, S-Expressions are nested lists of symbols. S-Expressions are used with languages that support the notion that code is data.

The many discussion postings on the Web regarding these topics would indicate a disconnect between the S-Expression and XML camps. The purpose of this article is to bridge the two worlds and offer a solution that addresses everyone's needs.

To illustrate the differences among the three syntaxes, let's start with a data structure expressed in XML S-Expressions, ConciseXML, and also a commonly used semicolon-delimited syntax used by many programming languages, including Java. While there are multiple ways of encoding the data in XML and S-Expressions, only one is shown for the purposes of the first comparison.

* XML



* S-Expressions

(book "0764525360" "Water Language" 2002)

* ConciseXML



* Semicolon-Delimited Syntax

new Book ("0764525360", "Water Language", 2002);

There are a number of similarities among the first three syntaxes:

* The expressions are delimited by characters that indicate the start and end of the expression. S-Expressions are delimited by a set of parentheses "( )", while XML and ConciseXML expressions use angle brackets " ".

* The expression name occurs immediately after the initial delimiter.

* White space is used to separate arguments.

* The syntax is independent of a specific language.

The semicolon-delimited syntax is different from the others in several ways. A comma is used between arguments, and there is no set of delimiter characters that always begin or end an expression. Parsing a semicolon-delimited syntax requires that the parser have language-specific knowledge. The first three syntaxes can be easily parsed, independent of any language.

Now let's look at some of the differences among the four...