5 ms·

Of course you can express anything on top of a relational model. But for graphs such a representation would have been awfully inefficient. For this reason, CADs

by sklogic 11y ago

Of course you can express anything on top of a relational model. But for graphs such a representation would have been awfully inefficient. For this reason, CADs never even tried to switch to a relational data storage once that fancy new relational databases appeared, most of the professional CADs are still using good old graph databases.

thesz 11y ago
I beg to disagree. I am part of the team developing Russian CAD system [0]. It uses what one can consider a hypergraph db (relation includes many objects), but that DBMS system has queries on par with SQL. And they prove themselves very useful in development of CAD. What you describe can be explained with development inertia. Most CADs are C/C++ and these languages are not very well suited for changes that go through all code base (change of storage engine and data model). I also made experiments during a dev of graph analytics engine in one part of my experience. The relational model (actually, linear algebra model) has proven itself very competitive. It allows for easy distribution of data, the operations over distributed data are close to optimal, etc, etc. [0] http://dd.ru/ http://dd.ru/
- sklogic 11y ago
  I worked on a (very old) ship-building and factory-building CAD, written mostly in PL/I and Fortran. It was built around a graph database. Throughout its long and turbulent history, there were many attempts of moving to a relational storage, every time resulting in orders of magnitude drop in performance. Keep in mind that in such a CAD designs are huge. Think of an aircraft carrier scale of "huge". And it was designed when memory was very limited. Therefore, pretty much all the CAD operations depended on the database access. So, nobody really cared about the queries, they were insignificant. What people cared about was: * Performance of following an arc * Transactions * Data consistency * Compactness of representation (remember, disk space is also a limited thing when you're building aircraft carriers). * Nice API (even in a very limited language)
  - thesz 11y ago
    Had the state of art changed from the time of their last attempt to move to relational DB? Had the hardware changed during that time? You tell us about some old project, written in hard to maintain languages, which had many failures to adapt to new tech. This is exactly what to expect. I am talking about relatively modern language (C#) using good DB tech (lagging about seven, maybe five years from the state of art). Maybe, the story will be different in our case.
    - sklogic 11y ago
      The last attempt was made in around 2008, AFAIR. Fundamentally nothing changed in the relational storage. Follow-a-graph-edge operation is as expensive as it used to be (involves an index lookup, it cannot be cheap). If you know a relational arrangement suitable for a cheap O(1) edge traversal - please share. But I am very skeptical. And I cannot see how the host language is relevant at all. C#, Haskell, whatever - none can make data access operations cost less than what the data model predicts.
      - thesz 11y ago
        Use covering indices for edges, it is vastly cheaper than regular indices. Choose write-optimized storage layer (fractal indices (circa ~2007, BTW!), LSM) for DB. Don't do singular accesses, use bulk accesses (and now we hit the wall of PL/1 and Fortran you mentioned). I can go on. I cannot help but feel that what you describe is a classic example of technical inertia due to massive technical debt. It cannot prove that relational DBs are bad for CADs.
        sklogic 11y ago
        Is any of the indices you're describing O(1)? Very, very unlikely. As for the bulk operations, they're in most cases totally useless. Rendering - maybe, but most of the other CAD operations require precise edge following. And why even going into all the troubles with using this totally unsuitable relational representation when a proper graph dbms is so much easier? Relational religion is so funny, almost as funny as OOP.

by sklogic 11y ago

thesz 11y ago

I beg to disagree. I am part of the team developing Russian CAD system [0]. It uses what one can consider a hypergraph db (relation includes many objects), but that DBMS system has queries on par with SQL. And they prove themselves very useful in development of CAD. What you describe can be explained with development inertia. Most CADs are C/C++ and these languages are not very well suited for changes that go through all code base (change of storage engine and data model). I also made experiments during a dev of graph analytics engine in one part of my experience. The relational model (actually, linear algebra model) has proven itself very competitive. It allows for easy distribution of data, the operations over distributed data are close to optimal, etc, etc. [0] http://dd.ru/ http://dd.ru/

sklogic 11y ago
I worked on a (very old) ship-building and factory-building CAD, written mostly in PL/I and Fortran. It was built around a graph database. Throughout its long and turbulent history, there were many attempts of moving to a relational storage, every time resulting in orders of magnitude drop in performance. Keep in mind that in such a CAD designs are huge. Think of an aircraft carrier scale of "huge". And it was designed when memory was very limited. Therefore, pretty much all the CAD operations depended on the database access. So, nobody really cared about the queries, they were insignificant. What people cared about was: * Performance of following an arc * Transactions * Data consistency * Compactness of representation (remember, disk space is also a limited thing when you're building aircraft carriers). * Nice API (even in a very limited language)
- thesz 11y ago
  Had the state of art changed from the time of their last attempt to move to relational DB? Had the hardware changed during that time? You tell us about some old project, written in hard to maintain languages, which had many failures to adapt to new tech. This is exactly what to expect. I am talking about relatively modern language (C#) using good DB tech (lagging about seven, maybe five years from the state of art). Maybe, the story will be different in our case.
  - sklogic 11y ago
    The last attempt was made in around 2008, AFAIR. Fundamentally nothing changed in the relational storage. Follow-a-graph-edge operation is as expensive as it used to be (involves an index lookup, it cannot be cheap). If you know a relational arrangement suitable for a cheap O(1) edge traversal - please share. But I am very skeptical. And I cannot see how the host language is relevant at all. C#, Haskell, whatever - none can make data access operations cost less than what the data model predicts.
    - thesz 11y ago
      Use covering indices for edges, it is vastly cheaper than regular indices. Choose write-optimized storage layer (fractal indices (circa ~2007, BTW!), LSM) for DB. Don't do singular accesses, use bulk accesses (and now we hit the wall of PL/1 and Fortran you mentioned). I can go on. I cannot help but feel that what you describe is a classic example of technical inertia due to massive technical debt. It cannot prove that relational DBs are bad for CADs.
      - sklogic 11y ago
        Is any of the indices you're describing O(1)? Very, very unlikely. As for the bulk operations, they're in most cases totally useless. Rendering - maybe, but most of the other CAD operations require precise edge following. And why even going into all the troubles with using this totally unsuitable relational representation when a proper graph dbms is so much easier? Relational religion is so funny, almost as funny as OOP.