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A "many to many" relationship is a term within the scope of mapping cardinality, also of schema designing as to an relational database(RDB). Such as one album has many tracks and otherwise one track can appear in more than one albums. This is a quite common phenomenon. For many-to-many relationships, It's determined to use a "relation set" spreadsheet for modeling instead of an "entity set" spreadsheet. So, in our process of CSV2RDF, we should distinguish between "entity set" and "relation set" if possible. In views of schema of an RDB, the fundamental difference between "entity set" and "relation set" can be seen from the composition of primary key of a spread sheet(or CSV table):
The significance of a relation set is, to contain the attributes that describe the relation, so in perspective of a triple of subject-predicate-object, the attributes of a relation set are like an expression of "adverbial"... Let's take some from TheSession DataBase for example:
<style> </style>
--we can see In this table, the <style> </style>
--we can see |
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To render "many to many" relationship with 2 methods:Let us convert the 3 rows of data from aforementioned excerpt of "recordings.csv" into(only choose columns--recording_id, track, number, tune_id): 1. Named Graph
If you upload it on Virtuoso, then you can query in SPARQL like this:
or refer to #98 (which however might be a hallucination) 2. Blank node
(That will directly impact our programing for CSV2RDF into Virtuoso.) |
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Hi Ich(@fujinaga ), it's so weird that I cannot upload the Named Graph content to Virtuoso (by putting them in a file with suffix .nq) But if I don't use the
Do you know why? |
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Any way, I put up the issue on openlink/virtuoso-opensource#1313. |
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How to deal with a "many to many" relationship from a RDB in our CSV2RDF work?
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