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

Answer 1

1) When you have to interchange your data with others. XML is the "lingua franca" of the Web -- just about everyone can read and interpret it, unlike a database file.

2) When your data volume is small and you don't have to do complex queries against it. XML files are good for things like storing configuration or document templates.

3) When you don't have many writers trying to access the same data. SQL databases have involved concurrency mechanisms that are working behind the scenes for you. SQL databases can support indexes for the retrieval of information on large data sets quickly...

Answer 2

I would go if I have limited mysql databases on my host, then I would see the opportunity for using XML as a datastore.

Answer 3

Whenever you don't have the luxury of having a database (think single user applications) or need a very lightweight storage format.

Also as the previous poster mentioned, an interchange format.

Answer 4

Both XML and RDMSs can be used as datastores, but each implementation has its own advantages and drawbacks.

Using XML to store data for a web application is usually not a big problem until you start dealing with large amounts of data or you decide that you want to discover other information from your data (example: data mining). In other words, storing large amounts of XML files for a datasource is not very scalable but it makes it easier to move the data around. XML can also be used to serialize complex objects in a non-relational format, which could eliminate the need for an ORM if you can serialize/deserialize your objects directly from the XML

RDMSs (databases) are usually more scalable, offer greater concurrency support and are much faster when working with large amounts of data. The relational model makes it easier to data mine later on. Databases do suffer from the object-relational impedance mismatch (http://en.wikipedia.org/wiki/Object-Relational_impedance_mismatch) which might require you to write ugly code or use complex ORMs.

Answer 5

I would never use any kind of XML to store my data.

We use XSLT transformations as a data abstraction layer in our SOA app. All objects send each other data in XSLT, so there is only one language they need to understand. Except for the database connector, which needs to be able to transform the data into SQL, for sending it to the DB.

This way you don't have SQL string generation distributed over a zillion objects in your app. Makes maintenance much easier.

Answer 6

Things I use XML for:

• Persisting an object hierarchy.
• Moving data from one process or machine to another.
• Data that changes rarely, if at all; configuration settings and the like.
• As the input to XSLT transforms: generally speaking, if one of my programs emits HTML, it's using XSLT to do it, and so the source data is going to represented as XML at some
• Text markup. (Let's not forget that!)

There's not a whole lot of overlap between those use cases and the use cases for a database. Some, but not much.

Ironically, where I'm making my heaviest use of XML at the moment is in a desktop app that builds an in-memory ADO DataSet and uses the DataSet's WriteXml and ReadXml methods to persist and retrieve it. I'm using ADO because it's whole lot easier to dynamically build a data model defined by metainformation using ADO than it would be to implement my own object model for the task.

So here's a case that looks like I'm using XML as a database. But I'm really not. I'm using an object model that happens to implement a lot of database-like functionality, and I'm using XML as its persistence format.