Variable structure in a DB table to be read in a Web form

Question

I have a "variable" structure to be put in a table DB. By "variable" I mean a sequence of couples field/value in which the "kind" of field determines the value type, I don't know exactly field order and I don't know how many times fields can repeat. Sometimes group of fields will repeat several times (it is a fiscal model).

Additional requirement: I should map these variable data into web page forms, handling some CRUD work. JQuery-ui, Struts 2, Hibernate. Preferred DBMS: MySQL.

The solutions I thought of:

1. vertical table. I could have some performance issue, which I could resolve with materialized views that "pivot" the rows in columns when I need massive data process. Not gone so far in this direction as it seems to be very expensive for development.
2. LOB fields. Pack my columns into one of those, perhaps having a "mapping" table to decode each column. My idea is to pull-out searchable fields as "real" columns in order to leave in the LOB just the less interesting mob of data and not to generate performance problems.
3. or better 2a. Use an xml inside the LOB field. This could be useful to pack/unpack data more comfortably, specially having to map data to a web form.

What do you think? And more, is there some way to create automatic views from xml fields? Or better to map such data to web form? I suspect Hibernate Tools won't work in any of the cases I described.

I hope I have been clear, it's still a bit confusing even to me :)

Answer 1

Your option 1 is the Entity-Attribute-Value antipattern.

See my answer to Product table, many kinds of product, each product has many parameters and my blog post EAV FAIL for alternatives and some reasons why EAV is wrong, at least for a relational database (I cover EAV in my book, SQL Antipatterns: Avoiding the Pitfalls of Database Programming ).

Also read this article about how a similar structure nearly doomed a company: Bad CaRMa .

Your options 2 & 3 are similar to described in How FriendFeed uses MySQL to store schema-less data . I don't know of any automatic way for an ORM to maintain that structure for you. You do have the chore of keeping your inverted index tables in sync with your LOB data.