Question

We have a large number of data in many categories with many properties, e.g.

category 1: Book

properties: BookID, BookName, BookType, BookAuthor, BookPrice

category 2: Fruit

properties: FruitID, FruitName, FruitShape, FruitColor, FruitPrice

We have many categories like book and fruit. Obviously we can create many tables for them (MySQL e.g.), and each category a table. But this will have to create too many tables and we have to write many “adapters” to unify manipulating data.

The difficulties are:

1) Every category has different properties and this results in a different data structure.

2) The properties of every categoriy may have to be changed at anytime.

3) Hard to manipulate data if each category a table (too many tables)

How do you store such kind of data?

Answer 1

You can separate the database into two parts: Definition Tables and Data Tables. Basically the Definition Tables is used to interpret the Data Tables where the actual data is stored (some would say that the definition tables is more elegant if represented in XML).

The following is the basic idea.

Definition Tables:

TABLE class  
class_id (int)  
class_name (varchar)

TABLE class_property  
property_id (int)  
class_id (int)  
property_name (varchar)  
property_type (varchar)  

Data Tables:

TABLE object  
object_id (int)  
class_id (varchar)  

TABLE object_property  
property_id (int)  
property_value (varchar) 

It would be best if you could also create additional Layer to interpret the structure so as to make it easier for the Data Layer to operate on the data. And you must of course take into consideration performance, ease of query, etc.

Just my two cents, I hope it could be of any help.

Regards.