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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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<HTML
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><HEAD
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><TITLE
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>Package Versioning</TITLE
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TITLE="The eCos Component Writer's Guide"
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TITLE="Package Organization"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>The <SPAN
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>eCos</SPAN
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> Component Writer's Guide</TH
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><TR
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><TD
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ALIGN="left"
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><A
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HREF="package.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 2. Package Organization</TD
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><TD
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="package.contents.html"
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>Next</A
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="PACKAGE.VERSIONS">Package Versioning</H1
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><P
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>Below each package directory there can be one or more version
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sub-directories, named after the versions. This is a requirement of
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the component framework: it must be possible for users to install
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multiple versions of a package and select which one to use for any
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given application. This has a number of advantages to users: most
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importantly it allows a single component repository to be shared
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between multiple users and multiple projects, as required; also it
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facilitates experiments, for example it is relatively easy to try out
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the latest version of some package and see if it makes any difference.
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There is a potential disadvantage in terms of disk space. However
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since <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> packages generally consist of source code intended for
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small embedded systems, and given typical modern disk sizes, keeping a
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number of different versions of a package installed will usually be
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acceptable. The administration tool can be used to remove versions
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that are no longer required.</P
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><DIV
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><A
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NAME="AEN217"><P
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></P
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><DIV
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CLASS="MEDIAOBJECT"
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><P
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><IMG
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SRC="version.png"
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ALIGN="CENTER"></P
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></DIV
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><P
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></P
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></DIV
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><P
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>The version <TT
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CLASS="FILENAME"
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>current</TT
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> is special. Typically it
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corresponds to the very latest version of the sources, obtained by
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anonymous <SPAN
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CLASS="APPLICATION"
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>CVS</SPAN
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>. These sources may change frequently, unlike full
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releases which do not change (or only when patches are produced).
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Component writers may also want to work on the
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<TT
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CLASS="FILENAME"
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>current</TT
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> version.</P
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><P
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>All other subdirectories of a package correspond to specific releases
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of that package. The component framework allows users to select the
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particular version of a package they want to use, but by default the
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most recent one will be used. This requires some rules for ordering
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version numbers, a difficult task because of the wide variety of ways
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in which versions can be identified.</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>The version <TT
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CLASS="FILENAME"
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>current</TT
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> is always considered to be
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the most recent version.</P
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></LI
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><LI
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><P
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>If the first character of both strings are either <TT
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CLASS="LITERAL"
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>v</TT
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>
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or <TT
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CLASS="LITERAL"
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>V</TT
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>, these are skipped because it makes little
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sense to enforce case sensitivity here. Potentially this could result
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in ambiguity if there are two version directories
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<TT
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CLASS="LITERAL"
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>V1.0</TT
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> and <TT
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CLASS="LITERAL"
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>v1.0</TT
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>, but this will
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match the confusion experienced by any users of such a package.
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However if two subsequent releases are called <TT
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CLASS="LITERAL"
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>V1.0</TT
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>
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and <TT
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CLASS="LITERAL"
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>v1.1</TT
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>, e.g. because of a minor mix-up when
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making the distribution file, then the case difference is ignored.</P
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></LI
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><LI
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><P
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>Next the two version strings are compared one character at a time.
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If both strings are currently at a digit then a string to number
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conversion takes place, and the resulting numbers are compared.
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For example <TT
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CLASS="LITERAL"
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>v10</TT
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> is a more recent release than
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<TT
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CLASS="LITERAL"
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>v2</TT
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>. If the two numbers are the same then processing
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continues, so for <TT
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CLASS="LITERAL"
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>v2b</TT
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> and <TT
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CLASS="LITERAL"
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>v2c</TT
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>
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the version comparison code would move on to <TT
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CLASS="LITERAL"
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>b</TT
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> and
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<TT
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CLASS="LITERAL"
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>c</TT
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>. </P
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></LI
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><LI
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><P
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>The characters dot <TT
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CLASS="LITERAL"
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>.</TT
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>, hyphen <TT
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CLASS="LITERAL"
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>-</TT
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>
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and underscore <TT
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CLASS="LITERAL"
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>_</TT
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> are treated as equivalent
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separators, so if one release goes out as <TT
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CLASS="LITERAL"
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>v1_1</TT
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> and
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the next goes out as <TT
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CLASS="LITERAL"
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>v1.2</TT
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> the separator has no
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effect.</P
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></LI
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><LI
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><P
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>If neither string has yet terminated but the characters are different,
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ASCII comparison is used. For example <TT
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CLASS="LITERAL"
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>V1.1b</TT
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> is
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more recent than <TT
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CLASS="LITERAL"
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>v1.1alpha</TT
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>.</P
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></LI
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><LI
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><P
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>If one version string terminates before the other, the current
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character determines which is the more recent. If the other string is
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currently at a separator character, for example
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<TT
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CLASS="LITERAL"
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>v1.3.1</TT
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> and <TT
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CLASS="LITERAL"
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>v1.3</TT
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>, then the former
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is assumed to be a minor release and hence more recent than the
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latter. If the other string is not at a separator character, for
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example <TT
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CLASS="LITERAL"
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>v1.3beta</TT
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>, then it is treated as an
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experimental version of the <TT
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CLASS="LITERAL"
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>v1.3</TT
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> release and hence
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older. </P
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></LI
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><LI
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><P
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>There is no special processing of dates, so with two versions
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<TT
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CLASS="LITERAL"
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>ss-20000316</TT
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> and <TT
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CLASS="LITERAL"
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>ss-20001111</TT
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>
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the numerical values <TT
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CLASS="LITERAL"
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>20001111</TT
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> and
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<TT
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CLASS="LITERAL"
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>20000316</TT
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> determine the result: larger values are
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more recent. It is suggested that the full year be used in such cases
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rather than a shorthand like <TT
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CLASS="LITERAL"
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>00</TT
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>, to avoid
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Y2100 problems.</P
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></LI
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><LI
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><P
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>There is no limit on how many levels of versioning are used, so
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there could in theory be a <TT
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CLASS="LITERAL"
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>v3.1.4.1.5.9.2.7</TT
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> release
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of a package. However this is unlikely to be of benefit to typical
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users of a package.</P
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></LI
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></OL
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><P
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>The version comparison rules of the component framework may not be
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suitable for every version numbering scheme in existence, but they
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should cope with many common cases.</P
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><DIV
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CLASS="CAUTION"
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><P
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></P
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CLASS="CAUTION"
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>Caution</B
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></TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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><P
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>There are some issues still to be resolved before it is possible to
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combine the <TT
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CLASS="FILENAME"
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>current</TT
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> sources available via
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anonymous <SPAN
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CLASS="APPLICATION"
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>CVS</SPAN
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> and full releases of <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> and additional packages in
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a single component repository. The first problem relates to the
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<SPAN
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CLASS="DATABASE"
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>ecos.db</SPAN
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> database: if a new package is added via
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the CVS repository then this requires a database update, but the
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administration tool is bypassed. The second problem arises if an
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organization chooses to place its component repository under source
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code control using <SPAN
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CLASS="APPLICATION"
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>CVS</SPAN
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>, in which case different directories will
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belong to different <SPAN
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CLASS="APPLICATION"
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>CVS</SPAN
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> servers. These issues will be addressed in a
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future release.</P
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>Prev</A
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HREF="cdl-guide.html"
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>Home</A
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ALIGN="left"
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>Package Organization</TD
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><TD
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ALIGN="center"
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HREF="package.html"
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>Up</A
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>Package Contents and Layout</TD
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