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Design Notes

[Motivation] [Design Goals/Requirements] [The Name 'Fardel'] [Structure] [Resource Names - The Programmer's View] [Locales - The Translator's View] [Fardel Resource-Scripts]

Motivation

While extending some small windows applications in C++, it became apparent that Microsoft Developer Studio (version 5) didn't have particularly good multi-language support:

• It is possible to create multiple copies of a string table and assign them different languages, however
  • The automatic lookup based on the local language only works under some win32 platforms
  • Other resource types (bitmaps, icons, dialog boxes etc) cannot be associated with a particular language
• Identification of resources is clumsy; non-string resources can be identified by name (string) or a number ; string resources must be identified by a number ; the resource compiler did not seem to cope with #define values for string identifiers.

A quick search found several approaches for C++/Java:

• Approach: Base class object with virtual functions for each resource ; language variants derive from this base class
  Drawbacks: Messages hard coded into program text ; major recompilation required each time a new message type (virtual function) is added
• Approach: Java PropertyResourceBundle class
  Drawbacks: Can only handle string resources
• Approach: Java ListResourceBundle class
  Drawbacks: Requires recompilation of program code; type checking is deferred to run-time, so type errors may be tricky to find

Design Goals/Requirements

Once the decision to create a language library was made, the following aims/requirements were adopted:

• The library would platform-independent as far as possible
• The library would package arbitrary binary resources
• There must be mechanisms for:
  • embedding a set of resources into a stand-alone program
  • embedding a set of resources into a (programming language independent) program-accessible resource file - see resource blob below
• Programming languages support should be considered for C, C++, Java, Perl.
  • Where resources are embedded in a stand-alone program, there must be some mechanism (as far as the programming language allows) for static type-checking of retrieved resources, the values passed as parameters to formatted string messages, and static existence checks that resources used are present.
  • There must be some mechanism for dynamic access to resources
• It should be easy to re-use

The Name 'Fardel'

The name chosen for the library was 'Fardel' - an archaic word meaning bundle or burden, from an Arabic word fard(a) meaning 'camel-load'.

Structure

Components in the system are:

• Fardel Resource-Scripts: human-readable text files containing embedded string resources and/or references to external resources (e.g. file name of an image, URL of a sound file)
• Fardel Resource-Script Compiler: compiles resource-scripts into blobs and/or code-fragments (see below)
• Blobs: a blob is a single file containing a collection of resources, generated by the script compiler from scripts
• Code-Fragments: generated by the Resource-Script Compiler, these are header/code files in some target programming language which allow resources to be incorporated into a stand-alone program
• Fardel Library Modules:
  • Support code linked into a stand-alone program
  • Routines for accessing resource blobs dynamically
  • Higher-level routines for string formatting etc

Resource Names - The Programmer's View

The idea behind multilanguage resources from a programmer's point of view is to hide the language-specific details of resources; the programmer tells the computer: "Display the 'file-not-found' error message in the local language".

Fardel provides a hierachical system of Resource Names which allows resources to be re-used in a number of projects. Resource Names have the following pattern:

• module.name

Some examples of Resource Names are:

• FileIO.OpenError
• FileIO.ReadError
• FileIO.CopiedOK
• Product.IconSmall
• Product.IconLarge
• Product.Version
• Product.FeedbackURL

The restrictions on the module.name patterns in Fardel resource-scripts are that they contain only printable unicode characters and use no ASCII punctutation characters apart from '-' (minus) and '_' (underscore). If you intend to generate code fragments to embed the resources within a program, the each pattern should be a valid, non-reserved identifier in the target programming language(s).

Locales - The Translator's View

From a translator's point of view, the task is to take resources - traditionally strings, but possibly also icons/images/sounds - given in one or more source languages and to produce their equivalents in a new language.

Fardel borrows the notion of a locale - a combined language-code and optional region-code - to capture the concept of a particular language. Locales are used many programming languages and operating systems. Some examples of locales are:

Locales can be used as a convenient way of providing defaults, with more specific language setting overriding more general settings. Using this, the resource list above becomes the following for Australian English:

• A list of ISO-639 language codes may be found at www.ics.uci.edu/pub/ietf/http/related/iso639.txt
• A list of ISO-3166 country codes may be found at www.chemie.fu-berlin.de/diverse/doc/ISO_3166.html

Fardel Resource-Scripts

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This page last changed: 21 May 2003 [Validate HTML]

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