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diff --git a/libjava/classpath/gnu/xml/aelfred2/package.html b/libjava/classpath/gnu/xml/aelfred2/package.html new file mode 100644 index 000000000..e20425844 --- /dev/null +++ b/libjava/classpath/gnu/xml/aelfred2/package.html @@ -0,0 +1,506 @@ +<!DOCTYPE html PUBLIC + '-//W3C//DTD XHTML 1.0 Transitional//EN' + 'http://www.w3.org/TR/xhtml1/DTD/transitional.dtd'> + +<html><head> + <title>package overview</title> +<!-- +/* + * Copyright (C) 1999,2000,2001 The Free Software Foundation, Inc. + */ +--> +</head><body> + +<p> This package contains Ælfred2, which includes an +enhanced SAX2-compatible version of the Ælfred +non-validating XML parser, a modular (and hence optional) +DTD validating parser, and modular (and hence optional) +JAXP glue to those. +Use these like any other SAX2 parsers. </p> + +<ul> + <li><a href="#about">About Ælfred</a><ul> + <li><a href="#principles">Design Principles</a></li> + <li><a href="#name">About the Name Ælfred</a></li> + <li><a href="#encodings">Character Encodings</a></li> + <li><a href="#violations">Known Conformance Violations</a></li> + <li><a href="#copyright">Licensing</a></li> + </ul></li> + + <li><a href="#changes">Changes Since the Last Microstar Release</a><ul> + <li><a href="#sax2">SAX2 Support</a></li> + <li><a href="#validation">Validation</a></li> + <li><a href="#smaller">You Want Smaller?</a></li> + <li><a href="#bugfixes">Bugs Fixed</a></li> + </ul></li> + +</ul> + +<h2><a name="about">About Ælfred</a></h2> + +<p>Ælfred is a XML parser written in the java programming language. + +<h3><a name="principles">Design Principles</a></h3> + +<p>In most Java applets and applications, XML should not be the central +feature; instead, XML is the means to another end, such as loading +configuration information, reading meta-data, or parsing transactions.</p> + +<p> When an XML parser is only a single component of a much larger +program, it cannot be large, slow, or resource-intensive. With Java +applets, in particular, code size is a significant issue. The standard +modem is still not operating at 56 Kbaud, or sometimes even with data +compression. Assuming an uncompressed 28.8 Kbaud modem, only about +3 KBytes can be downloaded in one second; compression often doubles +that speed, but a V.90 modem may not provide another doubling. When +used with embedded processors, similar size concerns apply. </p> + +<p> Ælfred is designed for easy and efficient use over the Internet, +based on the following principles: </p> <ol> + +<li> Ælfred must be as small as possible, so that it doesn't add too + much to an applet's download time. </li> + +<li> Ælfred must use as few class files as possible, to minimize the + number of HTTP connections necessary. (The use of JAR files has made this + be less of a concern.) </li> + +<li> Ælfred must be compatible with most or all Java implementations + and platforms. (Write once, run anywhere.) </li> + +<li> Ælfred must use as little memory as possible, so that it does + not take away resources from the rest of your program. (It doesn't force + you to use DOM or a similar costly data structure API.)</li> + +<li> Ælfred must run as fast as possible, so that it does not slow down + the rest of your program. </li> + +<li> Ælfred must produce correct output for well-formed and valid + documents, but need not reject every document that is not valid or + not well-formed. (In Ælfred2, correctness was a bigger concern + than in the original version; and a validation option is available.) </li> + +<li> Ælfred must provide full internationalization from the first + release. (Ælfred2 now automatically handles all encodings + supported by the underlying JVM; previous versions handled only + UTF-8, UTF_16, ASCII, and ISO-8859-1.)</li> + +</ol> + +<p>As you can see from this list, Ælfred is designed for production +use, but neither validation nor perfect conformance was a requirement. +Good validating parsers exist, including one in this package, +and you should use them as appropriate. (See conformance reviews +available at <a href="http://www.xml.com/">http://www.xml.com</a>) +</p> + +<p> One of the main goals of Ælfred2 was to significantly improve +conformance, while not significantly affecting the other goals stated above. +Since the only use of this parser is with SAX, some classes could be +removed, and so the overall size of Ælfred was actually reduced. +Subsequent performance work produced a notable speedup (over twenty +percent on larger files). That is, the tradeoffs between speed, size, and +conformance were re-targeted towards conformance and support of newer APIs +(SAX2), with a a positive performance impact. </p> + +<p> The role anticipated for this version of Ælfred is as a +lightweight Free Software SAX parser that can be used in essentially every +Java program where the handful of conformance violations (noted below) +are acceptable. +That certainly includes applets, and +nowadays one must also mention embedded systems as being even more +size-critical. +At this writing, all parsers that are more conformant are +significantly larger, even when counting the optional +validation support in this version of Ælfred. </p> + + +<h3><a name="name">About the Name <em>Ælfred</em></a></h3> + +<p>Ælfred the Great (AElfred in ASCII) was King of Wessex, and +some say of King of England, at the time of his death in 899 AD. +Ælfred introduced a wide-spread literacy program in the hope that +his people would learn to read English, at least, if Latin was too +difficult for them. This Ælfred hopes to bring another sort of +literacy to Java, using XML, at least, if full SGML is too difficult.</p> + +<p>The initial Æ ligature ("AE)" is also a reminder that XML is +not limited to ASCII.</p> + + +<h3><a name="encodings">Character Encodings</a></h3> + +<p> The Ælfred parser currently builds in support for a handful +of input encodings. Of course these include UTF-8 and UTF-16, which +all XML parsers are required to support:</p> <ul> + + <li> UTF-8 ... the standard eight bit encoding, used unless + you provide an encoding declaration or a MIME charset tag.</li> + + <li> US-ASCII ... an extremely common seven bit encoding, + which happens to be a subset of UTF-8 and ISO-8859-1 as well + as many other encodings. XHTML web pages using US-ASCII + (without an encoding declaration) are probably more + widely interoperable than those in any other encoding. </li> + + <li> ISO-8859-1 ... includes accented characters used in + much of western Europe (but excluding the Euro currency + symbol).</li> + + <li> UTF-16 ... with several variants, this encodes each + sixteen bit Unicode character in sixteen bits of output. + Variants include UTF-16BE (big endian, no byte order mark), + UTF-16LE (little endian, no byte order mark), and + ISO-10646-UCS-2 (an older and less used encoding, using a + version of Unicode without surrogate pairs). This is + essentially the native encoding used by Java. </li> + + <li> ISO-10646-UCS-4 ... a seldom-used four byte encoding, + also known as UTF-32BE. Four byte order variants are supported, + including one known as UTF-32LE. Some operating systems + standardized on UCS-4 despite its significant size penalty, + in anticipation that Unicode (even with surrogate pairs) + would eventually become limiting. UCS-4 permits encoding + of non-Unicode characters, which Java can't represent (and + XML doesn't allow). + </li> + + </ul> + +<p> If you use any encoding other than UTF-8 or UTF-16 you should +make sure to label your data appropriately: </p> + +<blockquote> +<?xml version="1.0" encoding="<b>ISO-8859-15</b>"?> +</blockquote> + +<p> Encodings accessed through <code>java.io.InputStreamReader</code> +are now fully supported for both external labels (such as MIME types) +and internal types (as shown above). +There is one limitation in the support for internal labels: +the encodings must be derived from the US-ASCII encoding, +the EBCDIC family of encodings is not recognized. +Note that Java defines its +own encoding names, which don't always correspond to the standard +Internet encoding names defined by the IETF/IANA, and that Java +may even <em>require</em> use of nonstandard encoding names. +Please report +such problems; some of them can be worked around in this parser, +and many can be worked around by using external labels. +</p> + +<p>Note that if you are using the Euro symbol with an fixed length +eight bit encoding, you should probably be using the encoding label +<em>iso-8859-15</em> or, with a Microsoft OS, <em>cp-1252</em>. +Of course, UTF-8 and UTF-16 handle the Euro symbol directly. +</p> + + +<h3><a name="violations">Known Conformance Violations</a></h3> + +<p>Known conformance issues should be of negligible importance for +most applications, and include: </p><ul> + + <li> Rather than following the voluminous "Appendix B" rules about + what characters may appear in names (and name tokens), the Unicode + rules embedded in <em>java.lang.Character</em> are used. + This means mostly that some names are inappropriately accepted, + though a few are inappropriately rejected. (It's much simpler + to avoid that much special case code. Recent OASIS/NIST test + cases may have these rules be realistically testable.) </li> + + <li> Text containing "]]>" is not rejected unless it fully resides + in an internal buffer ... which is, thankfully, the typical case. This + text is illegal, but sometimes appears in illegal attempts to + nest CDATA sections. (Not catching that boundary condition + substantially simplifies parsing text.) </li> + + <li> Surrogate characters that aren't correctly paired are ignored + rather than rejected, unless they were encoded using UTF-8. (This + simplifies parsing text.) Unicode 3.1 assigned the first characters + to those character codes, in early 2001, so few documents (or tools) + use such characters in any case. </li> + + <li> Declarations following references to an undefined parameter + entity reference are not ignored. (Not maintaining and using state + about this validity error simplifies declaration handling; few + XML parsers address this constraint in any case.) </li> + + <li> Well formedness constraints for general entity references + are not enforced. (The code to handle the "content" production + is merged with the element parsing code, making it hard to reuse + for this additional situation.) </li> + +</ul> + +<p> When tested against the July 12, 1999 version of the OASIS +XML Conformance test suite, an earlier version passed 1057 of 1067 tests. +That contrasts with the original version, which passed 867. The +current parser is top-ranked in terms of conformance, as is its +validating sibling (which has some additional conformance violations +imposed on it by SAX2 API deficiencies as well as some of the more +curious SGML layering artifacts found in the XML specification). </p> + +<p> The XML 1.0 specification itself was not without problems, +and after some delays the W3C has come out with a revised +"second edition" specification. While that doesn't resolve all +the problems identified the XML specification, many of the most +egregious problems have been resolved. (You still need to drink +magic Kool-Aid before some DTD-related issues make sense.) +To the extent possible, this parser conforms to that second +edition specification, and does well against corrected versions +of the OASIS/NIST XML conformance test cases. See <a href= +"http://xmlconf.sourceforge.net">http://xmlconf.sourceforge.net</a> +for more information about SAX2/XML conformance testing. </p> + + +<h3><a name="copyright">Copyright and distribution terms</a></h3> + +<p> +The software in this package is distributed under the GNU General Public +License (with a special exception described below). +</p> + +<p> +A copy of GNU General Public License (GPL) is included in this distribution, +in the file COPYING. If you do not have the source code, it is available at: + + <a href="http://www.gnu.org/software/classpath/">http://www.gnu.org/software/classpath/</a> +</p> + +<pre> + Linking this library statically or dynamically with other modules is + making a combined work based on this library. Thus, the terms and + conditions of the GNU General Public License cover the whole + combination. + + As a special exception, the copyright holders of this library give you + permission to link this library with independent modules to produce an + executable, regardless of the license terms of these independent + modules, and to copy and distribute the resulting executable under + terms of your choice, provided that you also meet, for each linked + independent module, the terms and conditions of the license of that + module. An independent module is a module which is not derived from + or based on this library. If you modify this library, you may extend + this exception to your version of the library, but you are not + obligated to do so. If you do not wish to do so, delete this + exception statement from your version. + + Parts derived from code which carried the following notice: + + Copyright (c) 1997, 1998 by Microstar Software Ltd. + + AElfred is free for both commercial and non-commercial use and + redistribution, provided that Microstar's copyright and disclaimer are + retained intact. You are free to modify AElfred for your own use and + to redistribute AElfred with your modifications, provided that the + modifications are clearly documented. + + This program is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + merchantability or fitness for a particular purpose. Please use it AT + YOUR OWN RISK. +</pre> + +<p> Some of this documentation was modified from the original +Ælfred README.txt file. All of it has been updated. </p> + +</p> + + +<h2><a name="changes">Changes Since the last Microstar Release</a></h2> + +<p> As noted above, Microstar has not updated this parser since +the summer of 1998, when it released version 1.2a on its web site. +This release is intended to benefit the developer community by +refocusing the API on SAX2, and improving conformance to the extent +that most developers should not need to use another XML parser. </p> + +<p> The code has been cleaned up (referring to the XML 1.0 spec in +all the production numbers in +comments, rather than some preliminary draft, for one example) and +has been sped up a bit as well. +JAXP support has been added, although developers are still +strongly encouraged to use the SAX2 APIs directly. </p> + + +<h3><a name="sax2">SAX2 Support</a></h3> + +<p> The original version of Ælfred did not support the +SAX2 APIs. </p> + +<p> This version supports the SAX2 APIs, exposing the standard +boolean feature descriptors. It supports the "DeclHandler" property +to provide access to all DTD declarations not already exposed +through the SAX1 API. The "LexicalHandler" property is supported, +exposing entity boundaries (including the unnamed external subset) and +things like comments and CDATA boundaries. SAX1 compatibility is +currently provided.</p> + + +<h3><a name="validation">Validation</a></h3> + +<p> In the 'pipeline' package in this same software distribution is an +<a href="../pipeline/ValidationConsumer.html">XML Validation component</a> +using any full SAX2 event stream (including all document type declarations) +to validate. There is now a <a href="XmlReader.html">XmlReader</a> class +which combines that class and this enhanced Ælfred parser, creating +an optionally validating SAX2 parser. </p> + +<p> As noted in the documentation for that validating component, certain +validity constraints can't reliably be tested by a layered validator. +These include all constraints relying on +layering violations (exposing XML at the level of tokens or below, +required since XML isn't a context-free grammar), some that +SAX2 doesn't support, and a few others. The resulting validating +parser is conformant enough for most applications that aren't doing +strange SGML tricks with DTDs. +Moreover, that validating filter can be used without +a parser ... any application component that emits SAX event streams +can DTD-validate its output on demand. </p> + +<h3><a name="smaller">You want Smaller?</a></h3> + +<p> You'll have noticed that the original version of Ælfred +had small size as a top goal. Ælfred2 normally includes a +DTD validation layer, but you can package without that. +Similarly, JAXP factory support is available but optional. +Then the main added cost due to this revision are for +supporting the SAX2 API itself; DTD validation is as +cleanly layered as allowed by SAX2.</p> + +<h3><a name="bugfixes">Bugs Fixed</a></h3> + +<p> Bugs fixed in Ælfred2 include: </p> + +<ol> + <li> Originally Ælfred didn't close file descriptors, which + led to file descriptor leakage on programs which ran for any + length of time. </li> + + <li> NOTATION declarations without system identifiers are + now handled correctly. </li> + + <li> DTD events are now reported for all invocations of a + given parser, not just the first one. </li> + + <li> More correct character handling: <ul> + + <li> Rejects out-of-range characters, both in text and in + character references. </li> + + <li> Correctly handles character references that expand to + surrogate pairs. </li> + + <li> Correctly handles UTF-8 encodings of surrogate pairs. </li> + + <li> Correctly handles Unicode 3.1 rules about illegal UTF-8 + encodings: there is only one legal encoding per character. </li> + + <li> PUBLIC identifiers are now rejected if they have illegal + characters. </li> + + <li> The parser is more correct about what characters are allowed + in names and name tokens. Uses Unicode rules (built in to Java) + rather than the voluminous XML rules, although some extensions + have been made to match XML rules more closely.</li> + + <li> Line ends are now normalized to newlines in all known + cases. </li> + + </ul></li> + + <li> Certain validity errors were previously treated as well + formedness violations. <ul> + + <li> Repeated declarations of an element type are no + longer fatal errors. </li> + + <li> Undeclared parameter entity references are no longer + fatal errors. </li> + + </ul></li> + + <li> Attribute handling is improved: <ul> + + <li> Whitespace must exist between attributes. </li> + + <li> Only one value for a given attribute is permitted. </li> + + <li> ATTLIST declarations don't need to declare attributes. </li> + + <li> Attribute values are normalized when required. </li> + + <li> Tabs in attribute values are normalized to spaces. </li> + + <li> Attribute values containing a literal "<" are rejected. </li> + + </ul></li> + + <li> More correct entity handling: <ul> + + <li> Whitespace must precede NDATA when declaring unparsed + entities.</li> + + <li> Parameter entity declarations may not have NDATA annotations. </li> + + <li> The XML specification has a bug in that it doesn't specify + that certain contexts exist within which parameter entity + expansion must not be performed. Lacking an offical erratum, + this parser now disables such expansion inside comments, + processing instructions, ignored sections, public identifiers, + and parts of entity declarations. </li> + + <li> Entity expansions that include quote characters no longer + confuse parsing of strings using such expansions. </li> + + <li> Whitespace in the values of internal entities is not mapped + to space characters. </li> + + <li> General Entity references in attribute defaults within the + DTD now cause fatal errors when the entity is not defined at the + time it is referenced. </li> + + <li> Malformed general entity references in entity declarations are + now detected. </li> + + </ul></li> + + <li> Neither conditional sections + nor parameter entity references within markup declarations + are permitted in the internal subset. </li> + + <li> Processing instructions whose target names are "XML" + (ignoring case) are now rejected. </li> + + <li> Comments may not include "--".</li> + + <li> Most "]]>" sequences in text are rejected. </li> + + <li> Correct syntax for standalone declarations is enforced. </li> + + <li> Setting a locale for diagnostics only produces an exception + if the language of that locale isn't English. </li> + + <li> Some more encoding names are recognized. These include the + Unicode 3.0 variants of UTF-16 (UTF-16BE, UTF-16LE) as well as + US-ASCII and a few commonly seen synonyms. </li> + + <li> Text (from character content, PIs, or comments) large enough + not to fit into internal buffers is now handled correctly even in + some cases which were originally handled incorrectly.</li> + + <li> Content is now reported for element types for which attributes + have been declared, but no content model is known. (Such documents + are invalid, but may still be well formed.) </li> + +</ol> + +<p> Other bugs may also have been fixed. </p> + +<p> For better overall validation support, some of the validity +constraints that can't be verified using the SAX2 event stream +are now reported directly by Ælfred2. </p> + +</body></html> + |