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What I always find hard to understand is that when you "query" a graph database, you have to start at a certain node. User: Name: John Age: 43 Count

by rb2k_ 15y ago

What I always find hard to understand is that when you "query" a graph database, you have to start at a certain node. User: Name: John Age: 43 Country: Sweden Job: SoftwareEngineer What if I wanted to get the names of all software engineers in sweden? Do I have to create a type of "job" node and start traversing from the one that is for software engineer's? Also: Is sorting possible at all with graph databases? What if I only want people called John that are older than 20? Is this too far out of scope for Graph Databases?

david927 15y ago
KayaDB is a graph database that can do that: It's a label directed graph that mimics the relational model, so you can do the things you mentioned but much more. For example, you can query just for John and it returns exact matches in any table/column in O(1).
- rb2k_ 15y ago
  Thanks for the information, but I'd rather not store my data somewhere that I can't get to or do local testing and development.
snprbob86 15y ago
"Is this too far out of scope for Graph Databases?" No, it's just that ad-hoc boolean queries are better suited for other query strategies. That's not to say that you couldn't use a graph database alongside another strategy. Neo4j, for example, has built in integration with Lucine. These sorts of boolean logic queries are best addressed by your typical b-tree index. Note that, in general, you want to prefer relationships over attributes. Depending on the application, you'd probably have something more like this: Node types: User(name, age) Country(name) Job(title) Relationship types: LivesIn() HasJob() To accomplish the boolean AND/OR queries, you'd store the key/value pairs from the User object from your comment in Lucine. But in the general cases of your app, you'd encode the relationships you need for particular, non-ad-hoc queries. Nodes and relationships can be used like pointers to create data structures in your graph. From there, standard algorithms generally apply. "Is sorting possible at all with graph databases" Often, you can completely bypass it by encoding order as a linked list. Add a relationship type: NextOldestPerson()
espeed 15y ago
Graph databases usually have an accompanying index. For example, Neo4j is tightly integrated with Lucene. You can use the index to get the start node, or you can reference the start node directly by using the node ID. If you have modeled the graph so that each Person node has a link (or "edge" in graph speak) labeled "location" that points to their country, then the Gremlin query to return all software engineers in Sweden would look like this: This is a Python example from the soon-to-be-released Bulbs persistence framework, which can connect to Neo4j, OrientDB, Dex, etc: sweden = Country.index.get(name="Sweden") script = "v.in('location'){it.occupation == 'Software Engineer'}" software_engineers = sweden.gremlin(Person,script=script) Here's what the code says: 1. Use the Country index to get the node with the name "Sweden". 2. Return a Gremlin query with results of type Person (software engineers) using the specified script. The script says, staring at vertex "v" (which is a reference to "self", which is in this case is sweden), return all the incoming vertices connected by an edge labeled "location" and filter the iterator by occupation ("it" is Gremlin for iterator), where occupation equals "Software Engineer". For more on graph data modeling, see "Knowledge Representation and Reasoning with Graph Databases" (http://markorodriguez.com/2011/02/23/knowledge-representation-and-reasoning-with-graph-databases/ http://markorodriguez.com/2011/02/23/knowledge-representatio...). Sorting is easy to do using Gremlin. Here's an example: g.v(1).out.sort{it.creation_date}.reverse().toList() This says in graph "g", start at vertex 1, return all of the outgoing vertices from vertex 1 and sort the results by creation_date, in reverse order, and return the results as a list. Gremlin is a domain specific language written in Groovy, and "it" means "iterator" in Groovy. Check out this post for more details on sorting (https://groups.google.com/forum/#!searchin/gremlin-users/sorting/gremlin-users/A8bZHSOxgyA/9Pyb2wl3I8YJ https://groups.google.com/forum/#!searchin/gremlin-users/sor...).

by rb2k_ 15y ago

david927 15y ago

KayaDB is a graph database that can do that: It's a label directed graph that mimics the relational model, so you can do the things you mentioned but much more. For example, you can query just for John and it returns exact matches in any table/column in O(1).

rb2k_ 15y ago
Thanks for the information, but I'd rather not store my data somewhere that I can't get to or do local testing and development.

snprbob86 15y ago

"Is this too far out of scope for Graph Databases?" No, it's just that ad-hoc boolean queries are better suited for other query strategies. That's not to say that you couldn't use a graph database alongside another strategy. Neo4j, for example, has built in integration with Lucine. These sorts of boolean logic queries are best addressed by your typical b-tree index. Note that, in general, you want to prefer relationships over attributes. Depending on the application, you'd probably have something more like this: Node types: User(name, age) Country(name) Job(title) Relationship types: LivesIn() HasJob() To accomplish the boolean AND/OR queries, you'd store the key/value pairs from the User object from your comment in Lucine. But in the general cases of your app, you'd encode the relationships you need for particular, non-ad-hoc queries. Nodes and relationships can be used like pointers to create data structures in your graph. From there, standard algorithms generally apply. "Is sorting possible at all with graph databases" Often, you can completely bypass it by encoding order as a linked list. Add a relationship type: NextOldestPerson()

espeed 15y ago

Graph databases usually have an accompanying index. For example, Neo4j is tightly integrated with Lucene. You can use the index to get the start node, or you can reference the start node directly by using the node ID. If you have modeled the graph so that each Person node has a link (or "edge" in graph speak) labeled "location" that points to their country, then the Gremlin query to return all software engineers in Sweden would look like this: This is a Python example from the soon-to-be-released Bulbs persistence framework, which can connect to Neo4j, OrientDB, Dex, etc: sweden = Country.index.get(name="Sweden") script = "v.in('location'){it.occupation == 'Software Engineer'}" software_engineers = sweden.gremlin(Person,script=script) Here's what the code says: 1. Use the Country index to get the node with the name "Sweden". 2. Return a Gremlin query with results of type Person (software engineers) using the specified script. The script says, staring at vertex "v" (which is a reference to "self", which is in this case is sweden), return all the incoming vertices connected by an edge labeled "location" and filter the iterator by occupation ("it" is Gremlin for iterator), where occupation equals "Software Engineer". For more on graph data modeling, see "Knowledge Representation and Reasoning with Graph Databases" (http://markorodriguez.com/2011/02/23/knowledge-representation-and-reasoning-with-graph-databases/ http://markorodriguez.com/2011/02/23/knowledge-representatio...). Sorting is easy to do using Gremlin. Here's an example: g.v(1).out.sort{it.creation_date}.reverse().toList() This says in graph "g", start at vertex 1, return all of the outgoing vertices from vertex 1 and sort the results by creation_date, in reverse order, and return the results as a list. Gremlin is a domain specific language written in Groovy, and "it" means "iterator" in Groovy. Check out this post for more details on sorting (https://groups.google.com/forum/#!searchin/gremlin-users/sorting/gremlin-users/A8bZHSOxgyA/9Pyb2wl3I8YJ https://groups.google.com/forum/#!searchin/gremlin-users/sor...).