Rough wind, that moanest loud
Grief too sad for song;
Wild wind, when sullen cloud
Knells all the night long;
Sad storm, whose tears are vain,
Bare woods, whose branches strain,
Deep caves and dreary main, -
Wail, for the world's wrong!
5. Encoding Recommendations
HTML allows more flexibility in principle and in practice than is
recommended here for encoding metadata. Limited flexibility
encourages easy development of software for extracting and processing
metadata. At this early evolutionary stage of internet metadata,
easy prototyping and experimentation hastens the development of
useful standards.
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Adherence is therefore recommended to the tagging style exemplified
in this document as regards prefix and element name capitalization,
double-quoting (") of attribute values, and not starting more than
one META tag on a line. There is much room for flexibility, but
choosing a style and sticking with it will likely make metadata
manipulation and editing easier. The following META tags adhere to
the recommendations and carry identical metadata in three different
styles:
Use of these recommendations is known to result in metadata that may
be harvested, indexed, and manipulated by popular, freely available
software packages such as [SWISH-E], [freeWAIS-sf2.0], [GLIMPSE],
[HARVEST], and [ISEARCH], among others. These conventions also work
with the metadata processing scripts appearing in the appendix, as
well as with most of the [DCPROJECTS] applications referenced from
the [DCHOME] site. Software support for the LINK tag and qualifier
conventions (see the next section) is not currently widespread.
Ordering of metadata elements is not preserved in general. Writers
of software for metadata indexing and display should try to preserve
relative ordering among META tagged elements having the same name
(e.g., among multiple authors), however, metadata providers and
searchers have no guarantee that ordering will be preserved in
metadata that passes through unknown systems.
6. Dublin Core in Real Descriptions
In actual resource description it is often necessary to qualify
Dublin Core elements to add nuances of meaning. While neither the
general principles nor the specific semantics of DC qualifiers are
within scope of this document, everyday uses of the qualifier syntax
are illustrated to lend realism to later examples. Without further
explanation, the three ways in which the optional qualifier syntax is
currently (subject to change) used to supplement the META tag may be
summarized as follows:
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Accordingly, a posthumous work in Spanish might be described with
Note that the qualifier syntax and label suffixes (which follow an
element name and a period) used in examples in this document merely
reflect current trends in the HTML encoding of qualifiers. Use of
this syntax and these suffixes is neither a standard nor a
recommendation.
7. Encoding Dublin Core Elements
This section consists of very simple Dublin Core encoding examples,
arranged by element.
Title (name given to the resource)
-----
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Creator (entity that created the content)
-------
Subject (topic or keyword)
-------
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Description (account, summary, or abstract of the content)
-----------
Publisher (entity that made the resource available)
---------
Contributor (other entity that made a contribution)
-----------
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Date (of an event in the life of the resource; [WTN8601] recommended)
----
Type (nature, genre, or category; [DCT1] recommended)
----
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Format (physical or digital data format, plus optional dimensions)
------
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Identifier (of the resource)
----------
Source (reference to the resource's origin)
------
Language (of the content of the resource; [RFC1766] recommended)
--------
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Relation (reference to a related resource)
--------
Coverage (extent or scope of the content)
--------
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Rights (text or identifier of a rights management statement)
------
8. Security Considerations
The syntax rules for encoding Dublin Core metadata in HTML that are
documented here pose no direct risk to computers and networks.
People can use these rules to encode metadata that is inaccurate or
even deliberately misleading (creating mischief in the form of "index
spam"), however, this reflects a general pattern of HTML META tag
abuse that is not limited to the encoding of metadata from the Dublin
Core set. Even traditional metadata encoding schemes (e.g., [MARC])
are not immune to inaccuracy, although they are generally followed in
environments where production quality greatly exceeds that of the
average Web site.
Systems that process metadata encoded with META tags need to consider
issues related to its accuracy and validity as part of their design
and implementation, and users of such systems need to consider the
design and implementation assumptions. Various approaches may be
relevant for certain applications, such as adding statements of
metadata provenance, signing of metadata with digital signatures, and
automating certain aspects of metadata creation; but these are far
outside the scope of this document and the underlying META tag syntax
that it describes.
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9. Appendix -- Perl Scripts that Manipulate HTML Encoded Metadata
This section contains two simple programs that work with versions 4
and 5 of the Perl [PERL] scripting language interpreter. They may be
taken and freely adapted for local organizational needs, research
proposals, venture capital bids, etc. A variety of applications are
within easy reach of implementors that choose to build on these
scripts.
Script 1: Metadata Format Conversion
-------------------------------------
Here is a simple Perl script that correctly recognizes every example
of metadata encoding in this document. It shows how a modest
scripting effort can produce a utility that converts metadata from
one format to another. Minor changes are sufficient to support a
number of output formats.
#!/depot/bin/perl
#
# This simple perl script extracts metadata embedded in an HTML file
# and outputs it in an alternate format. Issues warning about missing
# element name or value.
#
# Handles mixed case tags and attribute values, one per line or spanning
# several lines. Also handles a quoted string spanning multiple lines.
# No error checking. Does not tolerate more than one "From: Acting Shift Supervisor To: Plant Control Personnel RE: (--mbtitle) Date: (--mbfilemodtime)
Pursuant to directive DOH:10.2001/405aec of article B-2022, subsection 48.2.4.4.1c regarding staff morale and employee productivity standards, the current allocation of doughnut acquisition funds shall be increased effective immediately. Note that because replacement occurs throughout the document, the provider need only enter the title once instead of twice (normally the title must be entered once in the HTML head and again in the HTML body). After running the script, the above file is transformed into this:
From: Acting Shift Supervisor To: Plant Control Personnel RE: Nutritional Allocation Increase Date: 1999-03-08
Pursuant to directive DOH:10.2001/405aec of article B-2022,
subsection 48.2.4.4.1c regarding staff morale and employee
productivity standards, the current allocation of doughnut
acquisition funds shall be increased effective immediately.
Here is the script that accomplishes this transformation.
#!/depot/bin/perl
#
# This Perl script processes metadata block declarations of the form
# and variable references of the
# form (--mbVARNAME), replacing them with full metadata blocks and
# variable values, respectively. Requires a "template" file.
# Outputs an HTML file.
#
# Invoke this script with a single filename argument, "foo". It creates
# an output file "foo.html" using a temporary working file "foo.work".
# The size of foo.work is measured after variable replacement, and is
# later inserted into the file in such a way that the file's size does
# not change in the process. Has little or no error checking.
$infile = shift;
open(IN, "< $infile")
or die("Could not open input file \"$infile\"");
$workfile = "$infile.work";
unlink($workfile);
open(WORK, "+> $workfile")
or die("Could not open work file \"$workfile\"");
@offsets = (); # records locations for late size replacement
$title = ""; # gets the title during metablock processing
$language = "en"; # pre-set language here (not in the template)
$baseURL = "http://moes.bar.com/doh"; # pre-set base URL here also
$filename = "$infile.html"; # final output filename
$filesize = "(--mbfilesize)"; # replaced late (separate pass)
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($year, $month, $day) = (localtime( (stat IN) [9] ))[5, 4, 3];
$filemodtime = sprintf "%s-%02s-%02s", 1900 + $year, 1 + $month, $day;
sub putout { # outputs current line with variable replacement
if (! /\(--mb/) {
print WORK;
return;
}
if (/\(--mbfilesize\)/) # remember where it was
{ push @offsets, tell WORK; } # but don't replace yet
s/\(--mbtitle\)/$title/g;
s/\(--mblanguage\)/$language/g;
s/\(--mbbaseURL\)/$baseURL/g;
s/\(--mbfilename\)/$filename/g;
s/\(--mbfilemodtime\)/$filemodtime/g;
print WORK;
}
while (