Choice of database for a voting application

Question

I have seen a lot of topics asking for the choice of a database for a voting mechanism,but my inputs are a bit different. I have an application which contains a GUI in which there can be multiple fields/ radio button or a combination of the above. THe GUI is not fixed. Based on the form submitted, the answer XML is dynamically generated.

Thus if there is a form there can be 10000 different people submitting the same form . and i will be having 10000 different forms(numbers will increase).

I now have the following 2 options. Store every xml as it is in the database ( i have not made the choice of using a relational db or a nosql db like mongodb.) or parse the xml and create tables for every form. THat way the number of tables will be huge.

Now , I have to build a voting mechanism which basically looks at all the xml's that have been generated for a particular form i.e 10000 xml's and extract the answers submitted (Note: the xml is complex because 1 form can have multiple answer elements) and then do a vote to find how many people have given the same answer.

My Questions:

1. Should I use a relational db or NOSQL (MongoDB /Redis or similar ones)?
2. Do I need to save the xml documents as it is in the db or should I parse it and convert it to tables and save it? Any other approach that I can follow.

I am using JAVA/J2EE for devlepment currenty.

Answer 1

If your question is about how to store data of variable structure, then document database would be pretty handy. As it is schema-less, there will be no issues with rdbms columns maintenance.

Logically this way is pretty similar to storing xml in relational db. The difference is that with rdbms approach, each database reader should have a special xml parsing layer. (Also about xml you refer to Why would I ever choose to store and manipulate XML in a relational database?.)

In general, if you're planning to have a single database client, you can use xml/rdbms.

By the way, instead of storing xml, you can use rdbms in other way - define "generic" structure. For example, you can have "Entities (name, type, id)" table, and "Attributes (entityId, name, type, value)".

Answer 2

If you store XML in the DB - you gain flexibility against performance and maintainability (XML parsing with xpath etc can be verbose and error prone especially with complex and deeply nested XML structures)

If you store tables for each XML - you gain performance, ease of use, complexity against flexibility

Pick a hybrid approach. Store XMLs in a rdbms table as a generic XML structure (as suggested in one of the answers). This way you have fewer tables (less complexity) and avoid all the performance issue of XML parsing.