When would I use XML instead of SQL? [closed]

Answer 1

Here is an example of using XML with SQL: Authenticated users read and write data to various databases, not all of which are the same DBMS. Users for Company A use data from a local SQL Server database. Users for Company B use data from a remote Oracle database. And so on. A dozen different databases, each with slightly different schemas for the same basic data.

The website developer does not have the ability to create stored procedures on the remote databases. SQL must be sent directly from the web app to the database. Since each database has a slightly different SQL syntax and schema, it is necessary to use different SQL for each of the 12 databases for the same operation (SELECT, INSERT, etc).

One of the choices for embedding the SQL statements in the web app is to place them in XML files. Each XML file contains the set of SQL statements for one of the dozen databases. The code determines which database is accessed for the logged-in user, and retrieves the appropriate SQL from the specified XML file.

Just as with stored procedures, the SQL in the XML file can be updated without stopping or recompiling the application.

Answer 2

SQL is good tabular data -- data that easily fits into rows & columns. XML is good for hierarchical data -- data which has several levels of different sizes.

SQL is good for storage & searching. XML is good for transmitting & formatting.

Answer 3

Some applications use XML files to store configuration, I prefer to use SQLite to do so.

Answer 4

Use XML to create files that need to be sent to other applications. XML is more suited as data interchange format than as data storage format.

The following link is not bad to describe when using XML: Why should I use XML ?

Answer 5

To quote This Book (Effective XML: 50 Specific Ways to Improve Your XML):

“XML is not a database. It was never meant to be a database. It is never going to be a database. Relational databases are proven technology with more than 20 years of implementation experience. They are solid, stable, useful products. They are not going away. XML is a very useful technology for moving data between different databases or between databases and other programs. However, it is not itself a database. Don't use it like one.“

I think this sums it up, if a little bluntly. XML is a data interchange format. One can have XML parsing libraries that can query a DOM with XPath expressions but that is not the same thing as a DBMS. You can build a DBMS with a DOM/XPath interface but to get ACID properties or scale to large data sets you need to implement a DBMS engine and a data format with indexes, logging and other artifacts of a DBMS - which (by definition) makes it something other than XML.

Answer 6

I believe there are quite a few commercial applications that make heavy use of XML as a storage medium. I've done it for a project planning application, where the user stores each project in it's own file. The app lives on a USB stick, and requires zero install. All the data is pulled from the XML and worked on in memory, so getRecord(id) is nuts fast.

So my answer would be.. when the data is small enough to be held in memory, a database is over kill.