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%%____________________________________________________________________
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%% File: Introduction.tex
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%%____________________________________________________________________
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%%
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%% Author: Shaun ASHBY <Shaun.Ashby@cern.ch>
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%% Update: 2005-11-02 17:04:04+0100
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%% Revision: $Id$
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%%
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%% Copyright: 2005 (C) Shaun ASHBY
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%%
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%%--------------------------------------------------------------------
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\chapter{Introduction}\label{ch:intro}
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\index{Introduction}
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\scram\ has been developed to enable large, geographically dispersed
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and autonomous groups to work together on software development
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projects. The groups, primarily based in universities and academic
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institutions, independently manage their own resources. As such it can
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be extremely difficult or even impossible to impose software process,
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adequate documentation levels and heavy resource requirements - such
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as dedicating entire machines to a single software development
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project.
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\section{What is SCRAM?}\index{SCRAM!What is SCRAM?}
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\scram\ is a configuration management tool, a distribution system, a
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build system and resource manager, with local resources and
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applications managed in a transparent way. In addition it provides a
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common development environment. These features are described more
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fully below.
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\subsection{Configuration Management}\label{sec:cm}
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\index{SCRAM!configuration management}
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The main task of \scram\ is to ensure that all developers are working
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with the same consistent set of external products, libraries,
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environments and source codes. Configuration management methods ensure
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that this is possible.
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\begin{description}
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\item [\textsc{external products configuration}]\mbox{}\\
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A requirement of any \scram\ managed project is an explicit
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statement, in the form of a special-purpose document, of all
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underlying products and versions of external libraries and other
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software products used. Each product must have a description
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document to inform \scram\ how it is to be used, to supply dependency
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information, set environmental variables, and give default system
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locations. Such description documents can be maintained
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independently of \scram\ and imported into the project by
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\scram's built-in URL downloading mechanism.
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\item[\textsc{common configurations}]\mbox{}\\
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It is often the case that many projects need to share the same
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configuration in order that they can be inter-operable (\eg two
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applications using the same database). \scram\ thus provides a
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mechanism for importing independently maintained configuration
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documents automatically.
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\item[\textsc{source code control}]\mbox{}\\
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\scram\ itself is not a code repository. Any project must have
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access to one or more such repositories from which it can checkout
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the appropriate code into the appropriate place in the project
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structure. Currently, CVS is used for all source code management.
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Both source code and project configuration files are tagged with a
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CVS symbolic tag when ready for release.
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\item[\textsc{environment control}]\mbox{}\\
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The build and runtime environments are constructed automatically
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from the description documents of the required external products and
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the project-specific environment.
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\end{description}
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\subsection{The Distribution System}\label{sec:dist}
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\index{SCRAM!distribution system}
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\index{bootstrapping}
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\scram\ projects can be `bootstrapped' from a single description
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document in which the structure and download information of other
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required project documents and components is declared.
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\ni From this document \scram\ can construct a copy of a project release.
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Connected to a properly configured web browser such as Netscape makes
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automatic project installation possible. At present, \scram\ is unable
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to automatically install external components although the user can be
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directed to the correct documentation to enable him/her to do this.
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Binary distribution is not supported as building a distribution is
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seen as a check that all the components of the system have been
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installed properly. Other tools, compatible with \scram\, are available
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to produce binary distributions from project releases.
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\subsection{A System Resource/Application Interface}\label{sec:resource}
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\index{SCRAM!resource manager}
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\index{SCRAM!application interface}
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Often, machines are not installed with the various products in the
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same directories, their locations decided upon by system
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administrators or system constraints (sizes of filesystems, for
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example). Install locations can also vary from platform to platform.
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\scram\ matches up the request for a product in a project configuration
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to the system it is installing the project on. Automated means are
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used to achieve this but the user will be prompted if a product cannot
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be found. The user also can have full interactive control of these
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setup stages if preferred.
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\ni A database of system information is maintained by \scram\ for
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future reference in each project area.
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\subsection{A Build System}\label{sec:bs}
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\index{SCRAM!build system}
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The build system can be used to build shared or archive libraries,
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plug-in modules, binaries or additional libraries (for a test suite,
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for example). The configuration documents within the project area
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describe the actions to be taken during the build process. These
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actions can be global, or specific to parts of the source directory
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tree structure. (\eg everything in a directory \texttt{libsrc} could
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be automatically compiled into a library or every binary in a
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directory called \texttt{test} could be automatically linked with a
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test utilities library).
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\index{available library classes}
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\ni Classes of build objects can be defined: for example, a library class
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can have types such as {\em debug}, {\em archive}, {\em shared}, {\em
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shared debug}, \etc Default types can be assigned to a
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class/directory structure but can be easily overriden.% with options
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%from the command line.
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The environment can be easily tuned for
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special cases by simply modifying the templates defining the general
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rules. The dependencies are specified in an abstract manner. Extra
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external products to be included during linking can be referred to
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by name with \scram\ taking care of the system specifics.
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\index{module interfaces}
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\ni Module interfaces can be defined for large software modules to define
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dependencies \etc Other modules can then simply load the interface to
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use the module.
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\subsection{A Development Environment}\label{sec:de}
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\index{SCRAM!development environment}
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Once a copy of a project is installed and built on a particular
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platform it can be made publicly available (\ie {\em released}) for developers
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by adding it to \scram's list of projects (the project database).
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\ni Upon selecting an item from this list, a new development area is
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created in which the developer can work independently of everyone
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else. The development area will have the same configuration and
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environment as the base release. It will also automatically use
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libraries and headers from the base release if not rebuilt in the
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local development area.
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\subsection{Project Isolation}
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\index{SCRAM!project isolation}
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\scram\ ensures that an installed release is independent of any other.
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This allows developers to easily switch between projects/versions they
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might be working on even though they may have very different and
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conflicting environment requirements.
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%%
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\index{SCRAM!overview}
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\begin{latexonly}
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\begin{figure}[ht]
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\begin{center}
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\leavevmode \epsfig{file=images/scram.eps, width=\linewidth}
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\caption[A SCRAM overview.]
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{A SCRAM overview.}
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\label{f:SCRAM}
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\end{center}
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\end{figure}
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\end{latexonly}
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\ni In summary, \scram\ can provide
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\begin{itemize}
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\item project installation with a click on a web page;
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\item control of the build environment, including dependency tracking;
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\item fully configurable build operations, including default operations;
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\item abstraction of logical build elements from the implementation details;
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\item re-use of configuration management elements between projects.
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\end{itemize}
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\section{The Structure of This Guide}
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This document can be broken down as follows: firstly,
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Chapter~\ref{ch:install} gives some details on how to obtain \scram\
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and instructions on how to create a local installation.
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Chapter~\ref{ch:creatingprojects} contains all information necessary for
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administrators (or users wanting to use \scram\ privately) to
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create new projects using \scram\ as the management tool, and to
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maintain them. The various types of project configuration files, and
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the purposes of each (with use cases), are also described.
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Chapter~\ref{ch:examples} serves as a resource for developers who
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use \scram\ in their environment, providing some examples and tips covering topics
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like changing tool configurations or adding new external tools in a
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private area.
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\ni Finally there is a summary page containing help for usage for all of
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the currently supported \scram\ commands (p~\pageref{ch:quickhelpguide}).
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\newpage % Start on a fresh page
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%%% Local Variables:
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%%% mode: latex
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%%% TeX-master: "SCRAM-manual"
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%%% End:
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%%____________________________________________________________________
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%% End of Introduction.tex
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%%____________________________________________________________________
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%%
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