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    <p>If your data collection isn't too big, the <a href="http://en.wikipedia.org/wiki/Entity-attribute-value_model" rel="nofollow noreferrer"><strong>Entity-Attribute-Value</strong></a> (EAV) model may fit nicely the bill.</p> <p>In a nutshell, this structure allows the definition of <strong><em>Categories</em></strong>, the list of [required or optional] <strong><em>Attributes</em></strong> (aka properties) the entities in such category include etc, in a set of tables known as the <strong><em>meta-data</em></strong>, the logical schema of the data, if you will. The entity instances are stored in two tables a header and a values tables, whereby each attribute is stored in a single [SQL] record of the later table (aka "vertical" storage: what used to be a record in traditional DBMS model is made of several records of the value table).</p> <p>This format is very practical in particular for its flexibility: it allows both late and on-going changes in the logical schema (addition of new categories, additions/changes in the attributes of a given category etc.), as well the implicit data-driven handling of the underlying catalog's logical schema, at the level of the application. The main drawbacks of this format are the [somewhat] more sophisticated, abstract, implementation and, mainly, some limitations with regards to scaling etc. when the catalog size grows, say in the million+ entities range.</p> <p>See the EAV model described in more details in <a href="https://stackoverflow.com/questions/2350506/design-pattern-for-drilldown-filtered-search/2350532#2350532"><strong>this SO answer of mine</strong></a>.</p>
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    1. POhow to store data with many categories and many properties efficiently?
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    1. COEAV is the same thing with what Jaya Wijaya describes, isn't it?
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    2. CO@Mickey Shine: Yes, Jaya Wijaya's answers is an _example_ of EAV implementation. There can be many "twists" on this general basis, typically for performance purposes (for example having several possible columns in "object_property" table for the various value type (or possibly having several objet_property tables, one per tye etc, or also having some of the most common attributes stored in the object table rather than (or in addition to) the object_property table.. etc.), but on the whole these implementations share the same basic principle that the data is "stored vertically".
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    3. COYour answer makes me more clear about EAV. Thank you very much.
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