Internet-Draft M.T. Carrasco Benitez
<draft-carrasco-xdossier-00.txt> EMEA
Expires 29 February 1999 1 September 1999
Xdossier
Status of this memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
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Abstract
This is an informational memo for Xdossier. A Xdossier is a data
object designed for browsing with web browsers and mappable to XML. It
is based on a directory structure containing files in several formats.
Table of Contents
1. Introduction
2. Rationale
3. Terminology
4. Name
5. Representation
6. File extension
7. File formats
8. Character sets
9. Web Formats
10. Directory Index
11. Root directory
12. Well-formed and valid Xdossier
13. Xdossier DTD
13.1. By-Example Xdossier DTD
13.2. Syntactic Xdossier DTD
14. Self-containness
15. Compound Xdossier
16. Mapping
17. HTML for Index
18. References
19. Author
19.1. Disclaimer
1. Introduction
It is recommended to play with a Xdossier example, as this memo should
be easier to understand. For examples look in http://xdossier.com.
This recommendation is about organising files. They are organised into
a data object called Xdossier.
Informally, a Xdossier is a directory structure with files in several
formats created for web browsing; direct browsing ("file:") or served
browsing ("http:").
Classifying files within directories is easy and very instinctive. A
few HTML files with some descriptions and links can greatly help the
browsing and give a feel of "oneness". One can easily start organising
using the directory structure point of view. By following a few rules,
one can end up with a data object easy to browse and with a
significant structure.
A directory structure is a tree similar to an XML document. There is a
strong parallelism:
directory structure XML
------------------- ---
root directory document element/document entity
directory element
file entity
directory name element name
file name entity reference
content XML file parsed entity
content of non XML file unparsed entities
With a formal mapping to XML, the directory structure could be
transformed into an XML document.
A strategy could be to start with the (main) "tree" and to progress
with the organisation towards the content of the individual files (the
"leaves"): a few files could be XML files, eventually the whole
Xdossier should be transformable into a XML document.
This approach is particularly useful to organise large amount of
legacy data in several formats for which there is no clear formal
definition.
2. Rationale
- Usable with web browsers.
- Easy to "produce" and easy to "consume".
- Usable "as is" and adapted to further processing. For example, a CD-
ROM must be usable directly ("raw" consumption) and programs should be
capable of mechanical processing to load into a DBMS, web server, etc.
- Easy to prepare with resources (computer equipment, programs, staff,
etc) in most firms or acquirable at low cost. In particular, it should
be easy to prepare by hand without the need of special programs.
- Mappable to XML.
- Vendor independent.
- Usable as an interface to exchange data.
3. Terminology
The specific terms to this memo have usually the first character of
each token in capital.
- By-Example Xdossier DTD: A type of Xdossier DTD.
- By-Example DTD: Abbreviation of "By-Example Xdossier DTD".
- Directory Index: File, usually named "index.html", that contain
links to and information on files in a particular directory.
- Xdossier: (1) The concept as described in this memo. (2)
Abbreviation of "Xdossier Instance".
- Xdossier Instance: Parallel meaning with XML document instance.
- Xdossier Skeleton: A type of Xdossier DTD.
- Xdossier Table of Contents: The Xdossier in the root directory. The
Xdossier Table of Contents must allow the navigation of the whole
Xdossier. Typically, there would be links to other Directory Indexes.
- Index: Abbreviation of "Directory Index".
- Instance: Abbreviation of "Xdossier Instance".
- Skeleton: Abbreviation of "Xdossier Skeleton".
- Table of Contents: Abbreviation of "Xdossier Table of Contents".
4. Name
Xdossier that do not conform to this section are "Non-Naming
Conformant". Though all Xdossier must conform at least to the naming
in XML [XML].
"Name" is a token composed of the following characters:
- Letters "a" to "z"; i.e., lower case only; [U+0061 to U+007A].
- Digits "0" to "9" [U+0030 to U+0039].
- "-" [HYPHEN-MINUS, U+002D].
- "_" [LOW LINE, U+005F].
The notation "U+" refers to the Unicode [UNICODE] notation.
Correct Names
part_a
part-b
myfile
hello
Incorrect Names
part a (' ' ; SPACE is not allowed)
Myfile (capitals are not allowed)
myfile.xml ('.' ; FULL STOP is not allowed)
hello:html (':' ; COLON is not allowed)
"Directory Name" is a Name.
"File Name" is one Name followed by one or more Name(s) separated by a
'.' (FULL STOP, U+002E).
Correct File Names
a_part
myfile.html
hello.en.xml
hello.en.xml.gz
Incorrect Names
a part (' ' ; SPACE is not allowed)
Myfile.html (capitals are not allowed)
hello:xml (':' ; COLON is not allowed)
"Document Name" is the first Name in the File Name. Example, "docname"
in the File Name "docname.ext"
"File extension(s)" is/are the second and following Name(s). For
example, "ext1", "ext2" and "ext3" in the File Name
"docname.ext1.ext2.ext3"
5. Representation
The same information could be represented in different fashions. The
dimensions considered are:
- Language; e.g., English, Spanish.
- Media type; e.g., HTML, PDF.
- Encoding; e.g., gzip, compress.
6. File extension
File extensions are used to indicate representations. For example:
hello no extension
hello.html format HTML
hello.en language English
hello.gz compressed using "gzip"
hello.en.html English in HTML
hello.html.gz HTML, gziped
hello.en.gz English, gziped
hello.en.html.gz English, HTML, gziped
File extensions, particularly the last one, are operating systems
dependants:
- Syntax: e.g., DOS allows up to three characters file extensions.
- Association: which program is associated with the extension.
The extension should correspond to widely used mapping between
Internet Media Types [IMT] and file extensions. The examples above
work for transparent content negotiation in Apache.
Note the difference between "file" and "document". File refers to
physical storage; e.g., "mydoc.txt" is a file. Document refers to
content; e.g., "mydoc" is a document represented in the files
"mydoc.txt" and "mydoc.html", they contain the same document in
different formats.
Another memo should address the syntax for file extensions.
7. Format
Priority should be given to file formats (media types) with a good
chance of being readable "forever"; e.g., in 50 years. This points to
"neutral" formats: formal standard, industrial standard, vendor
independent, "text-like", etc.
One should not discard proprietary formats, as they could be the
"source" format; i.e., the format in which the data was originally
produced. Often, information is lost in format transformation. The
recommendation is to include:
- The source format.
- At least one neutral format.
- Indicate the method used in the format transformations; e.g. source
format saved HTML using the "Save as" facility in such application.
The file formats in order of preference are:
- Text: XHTML, HTML, XML, text, RTF and PDF.
- Graphic: JPEG, GIF and TIFF.
Other formats could also be included. They should be widely used
formats.
[Relation to Xdossier DTD]: It could include a list of accepted
formats in order of preference and different mapping between the
Internet Media Type and file extensions.
8. Character encoding
The character encoding ("charset") in order of preference are:
- Unicode UTF-8, Unicode 16 bits [ISO10646].
- ISO-8859-1 (Latin-1) or appropriate ISO-8859-x; e.g., ISO-8859-7 for
Greek.
Other character encoding could also be used. They should be widely
used character encoding.
[Relation to Xdossier DTD]: It could include a list of accepted
character encoding in order of preference.
9. Web Formats
These are file formats well adapted to the web and widely supported in
browsers; corollary: a very good format for the web, but not massively
supported in browsers is not a Web Format.
Web Format is a fuzzy moving definition. It is also "community
dependent"; e.g., a certain community could consider XML a Web Format
and another community could consider that it is not a Web Format.
By default, the only Web Format is HTML.
[Relation to Xdossier DTD]: It could redefine the list of Web Formats.
10. Directory Index
Directory Index, abbreviated to Index, is a document in Web Format
included in each directory.
There is a closed association among the directory, the Index in the
directory and the file(s). They refer to each other as "his". For
example, "Index and his directory and files".
Index should fulfil the dual function:
- Browsing (informal view).
- Metadata (formal view).
For browsing, Index should have a description of his directory and
meaningful labels with links to at least his file(s). It could also
contain links to other files/resources. Links to files within a
Xdossier must be relative. Whenever possible, links within a Xdossier
should point to an Index rather than a file.
For Metadata, Index should contain the metadata of his directory and
files. The metadata should be machine processable.
The browsing and metadata are functions. Syntactically, they could be
interwoven.
Syntactically, there are two types of Indexes:
- Informal Index: it does not follow any particular syntax.
- Formal Index: It follows a syntax.
If Index is not present, the File Names in the directory should be
meaningful.
The default Document Name for Index is "index" and the default format
is the default Web Format. Hence, at present the default File Name for
Index is "index.html".
Another memo should address the syntax for Formal Index.
[Relation to Xdossier DTD]: It could redefine the default Index name.
11. Root directory
The root directory must contain only one file, the Index; and zero or
more directories. Corollary: The trivial Xdossier is composed on one
Index.
The intention for allowing only one file in the root directory is to
make it obvious that the file present is the Table of Contents, as the
other elements must be directories.
12. Well-formed and valid Xdossier
Well-formed Xdossier is when it follows these recommendations. In
particular, it does not need a Xdossier DTD.
Valid Xdossier is when it is well-formed and in addition follows the
restrictions in a Xdossier DTD (By-Example DTD or Syntactic DTD).
13. Xdossier DTD
Xdossier DTD is needed for valid Xdossiers.
There is two type of Xdossier DTDs:
- "By-Example".
- " Syntactic".
13.1. By-Example Xdossier DTD
A Xdossier Instance could be a Xdossier DTD just by declaration that
it is a Xdossier DTD; i.e., follow "this example". Probably, some
aspects would be fuzzy.
More realistically, a By-Example DTD should be an "Xdossier Skeleton";
i.e., purpose built example. Typically, the files in the Skeleton
means that they must be present in the instantiations with the same
name and format. Additional instructions should be in the Indexes;
e.g. "such a file is optional".
People with limited knowledge in computers could create By-Example
DTDs, as it is instinctive. Probably, the path would be to create a
well-formed Instance and them to proceed with creation of a Skeleton.
As the approach does not have a fixed syntax, it is not intended for
full mechanical validation by computer. Some parts would have to be
validated by humans, though parts that follow a syntax could be
validated mechanically. For example, the content model of the
files/directories could be defined as:
- DTD: an XML DTD.
- Pair of values: for example a list of pair of values like
"/food/choco/index.html=Documents about chocolate"
13.2. Syntactic Xdossier DTD
This is needed to implement computer programs that could do full
mechanical validation of Xdossiers.
Another memo should address the syntax for Syntactic Xdossier DTD.
14. Self-containness
There are three levels:
- Absolute Xdossier: When all the resources are in the Xdossier.
- Self-Contain Xdossier: When all "Essential Resources" are in the
Xdossier. For example, the CSS is in the Xdossier, though there could
be secondary references to other resources such as a reference to the
W3C site at http://w3.org. At least this level should be attained.
- Fragment Xdossier: When at least one "Essential Resource" is not in
the Xdossier. For example, the CSS is not in the Xdossier and it
relies in an external CSS such as the one in the W3C site at
http://www.w3.org/StyleSheets/Core/. It is only recommended as a
directory of Xdossier. Otherwise, there should an agreement between
producers and consumers of the Xdossier.
Essential Resources are the ones needed for navigation and display.
[Relation to Xdossier DTD]: It could include the minimal level of
Self-containness requested and a re-definition of the Essential
Resources.
15. Compound Xdossier
It is a Xdossier where all the directories in the root directories are
Xdossier themselves. These directories could also be Compound
Xdossiers and so on.
[Relation to Xdossier DTD]: It could include require Compound
Xdossier.
16. Mapping
Mapping is for transforming between Xdossier and XML. Xdossier should
be transformable into XML.
Mapping:
directory <-> element
directory name <-> element name
root directory <-> document element
Index <-> attributes (for his directory and files)
file <-> entity
file name <-> entity name
file content <-> entity reference
XML file <-> Parsed entity
Non-XML file <-> Unparsed entity
17. HTML for Index
The HTML Indexes should follow the indications:
- Simple mainstream HTML; i.e., facilities easy to write and that work
in most browsers.
- XHTML [XHTML] approach. For example, well formed documents, separate
content from the presentation (e.g., CCS [CSS2]), etc.
- It is recommended to use one CSS for all the Indexes.
- A reasonable presentation with the most popular browsers (e.g.
Internet Explorer, Navigator, etc) and text only browsers (e.g. Lynx).
- Links that work when read directly (e.g., a CD-ROM inserted into a
PC) or served by an HTTP server; i.e., "file:" or "http:".
- Links that point directly to files, except when the intention is to
show the content of the directory. One should not assume that Xdossier
would be served by server; i.e., it should work directly ("file:") or
served ("http:").
- No frames, scripts (e.g. JavaScript) and Java Applets.
- Images (IMG) with alternative texts.
- Relative links within the Xdossier; e.g. href="../doc.html".
- Use language attributes (lang, xml:lang, etc), to indicate the
language of the text.
[Relation to Xdossier DTD]: It could change the HTML indications. In
particular, it could include at CSS for the Indexes.
18. References
[ALLEN] Package or Perish. Terry Allen
Pages 385-390 in SGML/XML '97 Conference Proceedings. SGML/XML '97.
[CML] Chemical Markup Language
http://www.venus.co.uk/omf/
[CSS2] Cascading Style Sheets, level 2
http://www.w3.org/TR/REC-CSS2
[DC] Dublin Core
http://purl.org/dc
[ISO10646] Information Technology -- Universal Multiple-Octet Coded
Character Set (UCS) -- Part 1: Architecture and Basic Multilingual
Plane, ISO/IEC 10646-1:1993
[HTML] HTML 4.0 Specification
http://www.w3.org/TR/REC-html40
[IMT] Internet Media Types
http://www.isi.edu/in-notes/iana/assignments/media-types/media-types
[MHTML] The MIME Multipart/Related Content-type. E. Levinson
ftp://ftp.ietf.org/rfc/rfc2387.txt
[RDF] Resource Description Framework Model and Syntax Specification
http://www.w3.org/TR/REC-rdf-syntax
[SCHEMA1] XML Schema Part 1: Structures ("work in progress")
http://www.w3.org/TR/xmlschema-1/
[Unicode] Unicode Consortium
http://www.unicode.org
[XDOSSIER-TRAN] Xdossier Transport ("work in progress")
http://xdossier.com
[XHTML] XHTML 1.0: The Extensible HyperText Markup Language ("work in
progress")
http://www.w3.org/TR/WD-html-in-xml
[XML] Extensible Markup Language (XML) 1.0
http://www.w3.org/TR/rec-xml
[XSL] Extensible Stylesheet Language Specification ("work in
progress")
http://www.w3.org/TR/WD-xsl
19. Author
Manuel Tomas CARRASCO BENITEZ
The European Agency for the Evaluation of Medicinal Products
7 Westferry Circus
Canary Wharf
London E14 4HB
U.K.
Telephone +44 171 418 86 45
carrasco@dragoman.org
http://dragoman.org/carrasco
19.1. Disclaimer
This memo represents only the view of the author.