md

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- The UNIX filesystem as an object store
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With MP3 we have ID3; i.e. a standard for metadata. Thus we have audio
file organizers like iTunes, Amarok, and Banshee.

But what about PDF files (research papers, books, manuals)? Images?
Movies? The situation isn't as nice for these.

With the UNIX filesystem, a general scheme for metadata storage can be
acheived.

Every file goes in it's own "object" directory.

Suppose I have 'avatar.avi'. A directory is created, the name of which
is a unique id:

    00000001

Inside that directory are various files:

    budget  data.avi  date  director  starring  title

The metadata was stored as such:

    $ echo 'Avatar'          >  title
    $ echo '2009'            >  date
    $ echo 'James Cameron'   >  director
    $ echo 'Sam Worthington' >  starring
    $ echo 'Zoe Saldana'     >> starring
    $ echo '237000000'       >  budget

All the "object" directories are kept under a single directory:

    00000001
    00000002
    00000003
    ...

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- Views into the object store
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OK, so how do you get to your data after it's placed into the store?

You generate a "view" into the store based on some criteria.

If I'm in the store directory, a very simple criteria is simply "*",
i.e. all the objects.

Here I'm going to generate a view intended for display by Emacs's Org
Mode:

    $ md-org-view *

This is what I see after the view is created:

    http://i.imgur.com/oqDid.png

Each item in the list is a hyperlink to the media file corresponding
to that object.

Let me generate a view of objects with 'Scheme' in the title:

    $ md-org-view `md-grep title Scheme`

The md-grep command outputs a list of object IDs. The md-org-view
command accepts a list of IDs.

Let's generate a view of objects authored by Chomsky:

    $ md-org-view `md-grep author Chomsky`

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- Directory views
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The 'md-dir-view' command creates a directory with links to data
files.

For example, let's say I want a view of objects with the file
extension 'mp3':

    $ cd $(md-dir-view `md-ext mp3`)

Or, a view of all pdf files, shown in nautilus:

    $ nautilus $(md-dir-view `md-ext pdf`)

This is an example of what you might see:

    http://i.imgur.com/tcf22.png

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- Importing objects
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Suppose you have a song stored as an MP3 which you want to import into
the object store. Instead of creating an object directory and
populating the metadata files manually, you can use an import utility
which gathers the metadata from the ID3 data or accesses a public
database such as MusicBrainz.

For movies, you can query a public database such as IMDB.

For academic papers, you can query CiteseerX or arXiv.

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