A Markup Database Interface; Borrowing from Groves

Hello all. I wanted to throw up an idea for a
XML interface to PostgreSQL.

The underlying information model for SGML documents
is called the "groves" model. The model's primary
prupose is to handle multiple content hierarchites
within a single network; as this is the primary
problem with multimedia hypertext markup (HyTime).
Anyway, what is interesting is that the core of the
groves model seems to be the following seemingly
simple production:

node := character | map( string, list(node) )

It is an alternation between a map (unordered
set) and a list (ordered bag). Anyway, the discovery
made me sit back in my chair and go hmmmmmm. As it
seems to me; this model is the essence of a multi-level
result set, and could point towards a rather natural
mapping of a multi-hierarchy result set onto a tag
based markup language like XML.

For starters, here is a row...

row-node := map (string, list(characters))

For example, here is an order, and two order-line rows:

order-row-node := { id = '345'
, buyer = 'Clark Evans'
}

order-line-row := { order-id = '345'
, product = 'Bag of rice'
, quantity = '1'
}

order-line-row := { order-id = '345'
, product = 'Tofo'
, quantity = '3'

And here, is a table:

relation-node := map('relation-name',list(row-node))

line-relation := { order-line =
[
{ order-id = '345'
, product = 'Bag of rice'
, quantity = '1'
}
,
...
,
{ order-id = '345'
, product = 'Tofo'
, quantity = '1'
}
]
}

Here is the origonal production again:

node := character | map( string, list(node) )

It could then be used to return a nested
result set like:

SELECT *
FROM ORDER
WHERE ID = '345'

with this sub-query nested...

SELECT PRODUCT, QUANTITY
FROM ORDER_LINE
WHERE ORDER_ID = ID;

my-order =: { id = '345'
, buyer = 'Clark Evans'
, lines =
[
{ order-id = '345'
, product = 'Bag of rice' }
, quantity = '1'
}
,
{ order-id = '345'
, product = 'Tofo'
, quantity = '3'
}
]
}

Here is a mapping to a simple markup language
(http://www.egroups.com/list/sml-dev/info.html)

<order>
<id>345</id>
<buyer>Clark Evans</buyer>
<order-line-list>
<order-line>
<product>Bag of rice</product>
<quantity>1</quantity>
</order-line>
<order-line>
<product>Tofo</product>
<quantity>3</quantity>
</order-line>
</order-line-list>
</order>

So, if you notice the even levels are maps,
and the odd levels are lists. Kinda cool.

Of course, you can shorten it with attribute notation...

<order id="345" buyer="Clark Evans">
<order-line product="Bag of rice" quantity="1" />
<order-line product="Tofo" quantity="3" />
</order>

(The syntax is more brief, but it only
allows for one list per map)

Anyway, this could allow for some nice automated
conversions in between a database and SML/XML/SGML.

Indeed, I was thinking that a binary version of
of the former syntax would make for a great
interface into/outof the database. Add a simple
text/binary adapter and PostgreSQL would be
XML ready... without the need for any particular
mapping tool.

Best,

Clark