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POBest practices to access schema-less data?
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copied!<p>I am toying with RDF, and in particular how to access information stored in a rdf storage. The huge difference from a traditional relational database is the lack of a predefined schema: in a relational database, you know that table has those columns, and you can technically map each row to an instance of a class. The class has well defined methods, and well defined attributes. </p> <p>In a schema-less system, you don't know what data is associated to a given information. It's like having a database table with an arbitrary and not predefined number of columns, and every row can have data in any number of these columns.</p> <p>Similar to ObjectRelational Mappers, there are Object RDF mappers. RDFAlchemy and SuRF are the two I am playing right now. Basically, they provide you a Resource object, whose methods and attributes are provided dynamically. It kind of make sense... however, it's not that easy. In many cases, you prefer to have a well defined interface, and to have more control of what's going on when you set and get data on your model object. Having such a generic access makes things difficult, in some sense.</p> <p>Another thing (and most important) I noted is that, even if <em>in</em> <em>general</em>, schema-less data are expected to provide arbitrary information about a resource, in practice you more or less know "classes of information" that tend to be together. Of course, you cannot exclude the presence of additional info, but this, in some cases, is the exception, rather than the norm, although the exception is sensible enough to be too disruptive for a strict schema. In a rdf representation of an article (e.g. like in RSS/ATOM feeds) you know the terms of your described resources, and you can map them to a well defined object. If you provide additional information, you can define an extended object (inherited from the base one) to provide accessors to the enhanced information. So in a sense, you deal with schema-less data by means of "schema oriented objects" you can extend <em>when</em> you want to see specific additional information you are interested about.</p> <p>My question is relative to your experience about real world usage practices of schema-less data storage. How do they map to the object-oriented world so that you can use it proficiently and without going too near to the "bare metal" of the schema-less storage ? (in RelDB terms, without using too much SQL and directly messing with the table structure)</p> <p>Is the access doomed to be very generic (e.g. SuRF "plugged-in attributes" is the highest, most specialized level you can have to access your data), or having specialized classes for specific agreed convenient schemas is also a good approach, introducing however the risk of having a proliferation of classes to access new and unexpected associated data ?</p>

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