I've been using python's sqlite bindings for my datasets (http://docs.python.org/library/sqlite3.html 
).  Using the format is just (bag_filename, field1, field2, field3,  
etc).  It's simple, short, sweet, and supports complicated queries.  ex:
conn = sqlite3.connect('/tmp/example')
c = conn.cursor()

c.execute('''create table stocks
  (date text, trans text, symbol text,
  qty real, price real)''')

c.execute("""insert into stocks
           values ('2006-01-05','BUY','RHAT',100,35.14)""")

conn.commit()
c.close()

-Hai

On Jun 21, 2010, at 10:05 PM, Tim Field wrote:

> Hi Ivan,
>
> I'm not sure it's possible to devise a meta-data schema flexible  
> enough to satisfy all use cases.  The ROS toolchain is pretty  
> flexible, though, and it should be easy to engineer a solution for  
> your particular needs.  The following techniques[*] might help you:
>
> To query the topics and message types in a bag, use:
>
>     rosbag info --yaml mybag.bag
>
> to return information about the bag in a YAML document.
>
> For arbitrary meta-data, it's easy to add any data you want to a  
> bag.  For example, here's a Python script that will take a bag  
> filename passed on the command-line, and add as the first message in  
> the bag a message on the /metadata topic:
>
>     import roslib; roslib.load_manifest('rosbag')
>     import sys, rosbag, rospy, std_msgs.msg
>     b = rosbag.Bag(sys.argv[1], 'a')
>
>     # @todo: generate your meta-data message here
>     metadata = std_msgs.msg.String()
>     metadata.data = 'my metadata'
>
>     for _, _, t in b.read_messages():
>         break
>     b.write('/metadata', metadata, t - rospy.Duration(0, 1))
>     b.close()
>
> For example, if you wanted to annotate the bag with a description  
> and keywords, the meta-data message could be populated from the  
> command-line arguments the user passes in.
>
> Your meta-data can then easily be read from the bag, either using  
> the rosbag API, or via the command-line, e.g.
>
>     rostopic echo -b metadata.bag -n 1 /metadata
>
> Tim
>
> [*] assuming a C-turtle installation
>
> On Mon, Jun 21, 2010 at 5:46 PM, Ivan Dryanovski <ivan.dryanovski@gmail.com 
> > wrote:
> Hi,
>
> We've been running into a somewhat logistical problem of having too
> many bag files, and no good way to organize them. Has anyone given
> thought to the idea of adding meta-data to the .bag files? It would be
> useful if we can attach a description and keywords so we can quickly
> find relevant bags. For example, you would keep all your bags in a
> specific directory, and have a ros tool that is able to search through
> them based on keywords, topics, or message types.
>
> Since adding explicit meta-data to the bag format might cause
> compatibility problems with current bag tools, perhaps a round-about
> solution would be to attach a "metadata" topic to each bag.
>
> Ivan Dryanovski
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