DRAFT: Astronomy Visualization Metadata Standard as a Microformat
1. Intended Scope of the AVM microformat
The Virtual Astronomy Multimedia Project (VAMP) project is currently defining metadata standards (AVM) to tag astronomical images (also known as 'pretty pictures') used for education and public outreach (EPO). The project will enable the creation of easily searchable databases of astronomical imagery. I wondered if the concept could be broadened out to the wider web of text, audio, and video in a more general way. This document shows my attempt to create an AVM microformat which is as close to the original AVM specifications (1.1) but within the constraints of HTML/CSS.
Using a microformat allows tagging to be included on web pages and in RSS feeds. That means that news and podcast feeds can be tagged too. Of course, the original specifications were for images of single objects so there are desirable features which are currently missing e.g. it would be useful to be able to specify a start and end time for an object within an audio/video podcast. Perhaps the VAMP team will change things in the future.
If you've never heard of microformats before you should probably go off and read about them first. They are part of the 'semantic' web and allow us to provide machine-readable information using the exisiting features of HTML and CSS. Existing microformat examples include hCard (a format for defining people, relationships and addresses) and rel="license" (used for Creative Commons licenses).
3. How to implement the AVM microformat
The easy way is to use the AVM microformat generator.
The harder way is to write it yourself. The AVM microformat attempts to stay as close to the specifications as possible however there is one minor change. The period (
.) used as a separator in the AVM tag names has been replaced by a hyphen (
-) as current web browsers (Firefox 2, Internet Explorer 7) are unable to parse class names containing periods (they are allowed in the specifications). Otherwise, most (all?) AVM tags should be directly portable.
To build the AVM microformat into your document you should first surround the object/image of interest with a
<span class="AVM"> tag e.g.
<span class="AVM"> NGC 7027 </span>
Next you should give the object a
Subject-Name. If the object is already a hyperlink this can be achieved by simply adding a
class="Subject-Name" attribute to the link. If it is not a link, a
<span class="Subject-Name"> can be included. e.g.
<span class="AVM"> <a href="http://www.google.com/" class="Subject-Name">NGC 7027</a> </span>or
<span class="AVM"> <span class="Subject-Name">NGC 7027</span> </span>
OK, we have now told a parser that the object exists and has a name. That isn't amazingly useful so lets add some more information such as its coordinates:
<span class="AVM"> <span class="Subject-Name">NGC 7027</span> (<span class="Spatial-ReferenceValue" title="316.7566375;+42.2361611"> 21h 07m 01.593s +42° 14' 10.18"</span>) </span>
Note that the coordinates have been displayed in a human readable form but the
title="316.7566375;+42.2361611" attribute of
<span class="Spatial-ReferenceValue"> has been used to provide the machine readable version. OK, let's add the
Spatial-Equinox to fully describe the coordinate system used for the position.
<span class="AVM"> <span class="Subject-Name">NGC 7027</span> <span class="Spatial"> (<span class="Spatial-ReferenceValue" title="316.7566375;+42.2361611"> 21h 07m 01.593s +42° 14' 10.18"</span> <span class="Spatial-CoordinateFrame">FK5</span> J<span class="Spatial-Equinox">2000.0</span>) </span> </span>
Hang on though, the output is now displayed as NGC 7027 B.4.1.3 (21h 07m 01.593s +42° 14' 10.18" FK5 J2000.0) . This sort of display could look very daunting to visitors who aren't astronomers. Let's hide all that extra information using the wonders of CSS.
<span class="AVM"> <span class="Subject-Name">NGC 7027</span> <span class="Spatial" style="display:none;"> (<span class="Spatial-ReferenceValue" title="316.7566375;+42.2361611"> 21h 07m 01.593s +42° 14' 10.18"</span> <span class="Spatial-CoordinateFrame">FK5</span> J<span class="Spatial-Equinox">2000.0</span>) </span> </span>
Tada! It should now display as NGC 7027. Much better.
4. Real-world Examples
The following paragraph shows how the AVM microformat can be applied inline within paragraphs. There are two microformat tagged objects in the paragraph. The first is NGC 7027 which has a
Subject-Category (styled to be hidden) and
Spatial entries added. The second object is Cygnus. It also has
Spatial-Equinox but these are hidden from normal display by using the CSS markup
style="display:none;" on the
Spatial span tag.
This beautiful image was taken by the NICMOS instrument onboard the Hubble Space Telescope in 1998. It shows an object named NGC 7027 (21h 07m 01.593s +42° 14' 10.18" FK5 J2000.0) - a planetary nebula - which is about 15 arcseconds in diameter (about a 120th of the angular diameter of the Moon) that can be found in the direction of Cygnus the Swan.
This example takes a data table included at the bottom of a Chandra X-ray telescope press release page. First I will show the orginal HTML of the table.
If we now apply the microformat markup we should get something that looks very similar but with all the extra information provided for machine reading.