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