147 lines
6.8 KiB
HTML
147 lines
6.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!--
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(C) Copyright 2002-4 Robert Ramey - http://www.rrsd.com .
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Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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-->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<link rel="stylesheet" type="text/css" href="../../../boost.css">
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<link rel="stylesheet" type="text/css" href="style.css">
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<title>Serialization - Overview</title>
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</head>
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<body link="#0000ff" vlink="#800080">
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary="header">
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<tr>
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<td valign="top" width="300">
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<h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3>
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</td>
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<td valign="top">
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<h1 align="center">Serialization</h1>
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<h2 align="center">Overview</h2>
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</td>
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</tr>
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</table>
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<hr>
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<dl class="index">
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<dt><a href="#Requirements">Requirements</a></dt>
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<dt><a href="#otherimplementations">Other Implementations</a></dt>
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</dl>
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<p>Here, we use the term <strong>"serialization"</strong> to mean
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the reversible deconstruction of an arbitrary set of C++ data structures
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to a sequence of bytes. Such a system can be used to reconstitute
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an equivalent structure in another program context. Depending on
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the context, this might used implement object persistence, remote
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parameter passing or other facility. In this system we use the term
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<strong>"archive"</strong> to refer to a specific rendering of this
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stream of bytes. This could be a file of binary data, text data,
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XML, or some other created by the user of this library.
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<h2><a name="Requirements"></a>Our goals for such a system are:</h2>
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<ol>
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<li>Code portability - depend only on ANSI C++ facilities.
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<li>Code economy - exploit features of C++ such as RTTI,
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templates, and multiple inheritance, etc. where appropriate to
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make code shorter and simpler to use.
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<li>Independent versioning for each class definition. That
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is, when a class definition changed, older files can still be
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imported to the new version of the class.
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<li>Deep pointer save and restore. That is, save and restore
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of pointers saves and restores the data pointed to.
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<li>Proper restoration of pointers to shared data.
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<li>Serialization of STL containers and other commonly used
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templates.
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<li>Data Portability - Streams of bytes created on one platform
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should be readable on any other.
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<li>Orthogonal specification of class serialization and archive format.
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That is, any file format should be able to store serialization
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of any arbitrary set of C++ data structures without having to
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alter the serialization of any class.
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<li>Non-intrusive. Permit serialization to be applied to
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unaltered classes. That is, don't require that classes to be
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serialized be derived from a specific base class or implement
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specified member functions. This is necessary to easily
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permit serialization to be applied to classes from class
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libraries that we cannot or don't want to have to alter.
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<li> The <strong>archive</strong> interface must be simple
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enough to easily permit creation of a new type of archive.
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<li> The <strong>archive</strong> interface must be rich
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enough to permit the creation of an <strong>archive</strong>
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that presents serialized data as XML in a useful manner.
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</ol>
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<h2><a name="otherimplementations"></a>Other implementations</h2>
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Before getting started I searched around for current
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implementations. I found several.
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<ul>
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<li><u>MFC</u> This is the one that I am very familiar with.
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I have used it for several years and have found it very useful.
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However it fails requirements 1, 2, 3, 6, 7, and 9. In spite
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of all the requirements not fulfilled, this is the most
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useful implementation I've found. It turns out that class
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versioning - partially implemented in MFC - really is
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indispensable for my applications. Inevitably, version 1.x of
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a shipping program needs to store more information in files
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than was originally provided for. MFC is the only one of these
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implementations that supports this - though only for the most
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derived class. Still it's better than nothing and does the
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job. MFC doesn't implement serialization of STL collections.
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Though it does so for MFC collections.
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<li><u>CommonC++ libraries</u> <a href="bibliography.html#1">[1]</a>
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As far as I can tell, this
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closely follows the MFC implementation but does address a few
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of the issues. It is portable and creates portable archives but
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skips versioning. It does support proper and complete
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restoration of pointers and STL collections. It does address
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compression though not in the way that I would prefer. The
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package would also benefit from having better documentation.
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So it fails to address 2, 3, 7, 8, and 9.
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<li><u>Eternity</u> <a href="bibliography.html#2">[2]</a>
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This is a bare bones package. It
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seems well coded but it really needs documentation and
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examples. It's not obvious how to use it without time
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consuming study of the source code. Recent versions do support
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files in XML format. This Fails 3, 6, 7?, 8, and 9.
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<li><u>Holub's implementation</u> <a href="bibliography.html#3">[3]</a> This is the article that
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first got me thinking about my own requirements for
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a serialization implementation. Interesting and worth
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the read if you can overlook the arrogant tone of the prose.
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This implementation fails 2, 3, 4, 5, and 6.
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<li><u>s11n</u> <a href="bibliography.html#13">[13]</a>
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This library has similar goals to this one. Some aspects of the
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implemenation are also similar. As of this writing, it would seem that:
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<ul>
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<li>Portability(1) is guarenteed only for recent versions of GCC.
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<li>Versioning(3) of class definitions is not explicitly supported by
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the library.
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<li>it doesn't seem to automatically account for shared pointers(5).
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I concluded this from the documentation as well as the statement that
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serialization of graph like structures is not supported.
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</ul>
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Its has lots of differences - and lots in common with this implementation.
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</ul>
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<hr>
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<p>Revised 1 November, 2004
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<p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004.
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Distributed under the Boost Software License, Version 1.0. (See
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accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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</i></p>
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</body>
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</html>
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