[sakai2-tcc] [Building Sakai] Assignments Shows Wrong Submission For Student

[David Adams]

Steve Swinsburg wrote:
> In Oracle, the XMLTYPE allows for direct querying of the XML within the
> database, and many other powerful actions.

No matter how efficient, storing XML-as-XML introduces a lot more
overhead than just storing the fields-as-fields. Offloading the XML
parsing to the database would make some things more efficient, but it
would partially just move CPU and memory load from the easier-to-scale
app servers to the harder-to-scale database server. Unless we're
working with XML for some specific purpose, then using XML at all is a
huge waste of resources.

> Then you don't need to worry about database upgrades if you want to
> add another column, the data just going into the XML and you work
> with it.

This is not true, and it's a poisonous myth to propagate. Transitions
are inevitable no matter what your data format. Yes, just adding a
field to XML on the fly in your code is easy enough, but so is running
ALTER TABLE ADD COLUMN. To use that new field, you have to build
indexes and views in either situation. And if a data field needs to be
broken out into another structure or converted to a different type,
you still have to either update every record in the database with the
new format, or put complicated and risky logic in your code to
accomodate the multiple possible formats.

Not to mention that the schema of an existing database often serves as
the best description of its structure, better than any outdated,
mistake filled, human generated documentation. An RDBMS schema is
provides free reflection to ORM tools and the like, not to mention
human troubleshooters. With a schema-less format, you completely lose
that benefit. If you force your XML to conform to DOCTYPEs or XML
Schemas, suddenly you're back to writing DDL and dealing with schema
upgrades, only with a much more complicated language that fewer people
understand.

> You can create a dynamic view from that info for faster data access,
> if required.

Again, this is extra work to get parity with storing data in
relational form. And for the questionable benefit of being able to say
your RDBMS supports XML natively. When we're using XML only as a
serialization format in Sakai, all we've done is to add extra
processing to both create the XML on app server and to parse it on the
database server, creating a lot of extra work in the data layer, for
administrators and DBAs, all for the sake of avoiding writing some
boring DDL and checking the "XML" box.

-dave