Hi Marko,
I will respond in more detail tomorrow (I'm a late-night-thinking,
early-morning-writing kind of guy) but yes I think this is cool, so long as
we are not overloading the steps with different levels of abstraction.
A has("age",
29), for example, operates at a different level of abstraction than a
has("city",
"Santa Fe") if "city" is a column in an "addresses" table. At least, they
are different if the data model allows for multi-properties,
meta-properties, and hyper-edges. A property is something that can either
be there, attached to an element, or not be there. There may also be more
than one such property, and it may have other properties attached to it. A
column of a table, on the other hand, is always there (even if its value is
allowed to be null), always has a single value, and cannot have further
properties attached. The same goes for values().
In order to simplify user queries, you can let has() and values() do double
duty, but I still feel that there are lower-level operations at play, at a
logical level even if not at a bytecode level. However, expressing the a
traversal in terms of its lowest-level relational operations may also be
useful for query optimization.
Josh
On Mon, Apr 29, 2019 at 7:34 AM Marko Rodriguez <[email protected]>
wrote:
> Hi,
>
> *** This email is primarily for Josh (and Kuppitz). However, if others are
> interested… ***
>
> So I did a lot of thinking this weekend about structure/ and this morning,
> I prototyped both graph/ and rdbms/.
>
> This is the way I’m currently thinking of things:
>
> 1. There are 4 base types in structure/.
> - Primitive: string, long, float, int, … (will constrain
> these at some point).
> - TTuple<K,V>: key/value map.
> - TSequence<V>: an iterable of v objects.
> - TSymbol: like Ruby, I think we need “enum-like” symbols
> (e.g., #id, #label).
>
> 2. Every structure has a “root.”
> - for graph its TGraph implements TSequence<TVertex>
> - for rdbms its a TDatabase implements
> TTuple<String,TTable>
>
> 3. Roots implement Structure and thus, are what is generated by
> StructureFactory.mint().
> - defined using withStructure().
> - For graph, its accessible via V().
> - For rdbms, its accessible via db().
>
> 4. There is a list of core instructions for dealing with these
> base objects.
> - value(K key): gets the TTuple value for the provided key.
> - values(K key): gets an iterator of the value for the
> provided key.
> - entries(): gets an iterator of T2Tuple objects for the
> incoming TTuple.
> - hasXXX(A,B): various has()-based filters for looking
> into a TTuple and a TSequence
> - db()/V()/etc.: jump to the “root” of the withStructure()
> structure.
> - drop()/add(): behave as one would expect and thus.
>
> ————
>
> For RDBMS, we have three interfaces in rdbms/.
> (machine/machine-core/structure/rdbms)
>
> 1. TDatabase implements TTuple<String,TTable> // the root
> structure that indexes the tables.
> 2. TTable implements TSequence<TRow<?>> // a table is a sequence
> of rows
> 3. TRow<V> implements TTuple<String,V>> // a row has string column
> names
>
> I then created a new project at machine/structure/jdbc). The classes in
> here implement the above rdbms/ interfaces/
>
> Here is an RDBMS session:
>
> final Machine machine = LocalMachine.open();
> final TraversalSource jdbc =
> Gremlin.traversal(machine).
> withProcessor(PipesProcessor.class).
> withStructure(JDBCStructure.class,
> Map.of(JDBCStructure.JDBC_CONNECTION, "jdbc:h2:/tmp/test"));
>
> System.out.println(jdbc.db().toList());
> System.out.println(jdbc.db().entries().toList());
> System.out.println(jdbc.db().value("people").toList());
> System.out.println(jdbc.db().values("people").toList());
> System.out.println(jdbc.db().values("people").value("name").toList());
> System.out.println(jdbc.db().values("people").entries().toList());
>
> This yields:
>
> [<database#conn1: url=jdbc:h2:/tmp/test user=>]
> [PEOPLE:<table#PEOPLE>]
> [<table#people>]
> [<row#PEOPLE:1>, <row#PEOPLE:2>]
> [marko, josh]
> [NAME:marko, AGE:29, NAME:josh, AGE:32]
>
> The bytecode of the last query is:
>
> [db(<database#conn1: url=jdbc:h2:/tmp/test user=>), values(people),
> entries]
>
> JDBCDatabase implements TDatabase, Structure.
> *** JDBCDatabase is the root structure and is referenced by db()
> *** (CRUCIAL POINT)
>
> Assume another table called ADDRESSES with two columns: name and city.
>
>
> jdbc.db().values(“people”).as(“x”).db().values(“addresses”).has(“name”,eq(path(“x”).by(“name”))).value(“city”)
>
> The above is equivalent to:
>
> SELECT city FROM people,addresses WHERE people.name=addresses.name
>
> If you want to do an inner join (a product), you do this:
>
>
> jdbc.db().values(“people”).as(“x”).db().values(“addresses”).has(“name”,eq(path(“x”).by(“name”))).as(“y”).path(“x”,”y")
>
> The above is equivalent to:
>
> SELECT * FROM addresses INNER JOIN people ON people.name=addresses.name
>
> NOTES:
> 1. Instead of select(), we simply jump to the root via db() (or
> V() for graph).
> 2. Instead of project(), we simply use value() or values().
> 3. Instead of select() being overloaded with by() join syntax, we
> use has() and path().
> - like TP3 we will be smart about dropping path() data
> once its no longer referenced.
> 4. We can also do LEFT and RIGHT JOINs (haven’t thought through
> FULL OUTER JOIN yet).
> - however, we don’t support ‘null' in TP so I don’t know
> if we want to support these null-producing joins. ?
>
> LEFT JOIN:
> * If an address doesn’t exist for the person, emit a “null”-filled
> path.
>
> jdbc.db().values(“people”).as(“x”).
> db().values(“addresses”).as(“y”).
> choose(has(“name”,eq(path(“x”).by(“name”))),
> identity(),
> path(“y”).by(null).as(“y”)).
> path(“x”,”y")
>
> SELECT * FROM addresses LEFT JOIN people ON people.name=addresses.name
>
> RIGHT JOIN:
>
> jdbc.db().values(“people”).as(“x”).
> db().values(“addresses”).as(“y”).
> choose(has(“name”,eq(path(“x”).by(“name”))),
> identity(),
> path(“x”).by(null).as(“x”)).
> path(“x”,”y")
>
>
> SUMMARY:
>
> There are no “low level” instructions. Everything is based on the standard
> instructions that we know and love. Finally, if not apparent, the above
> bytecode chunks would ultimately get strategized into a single SQL query
> (breadth-first) instead of one-off queries (depth-first) to improve
> performance.
>
> Neat?,
> Marko.
>
> http://rredux.com <http://rredux.com/>
>
>
>
>
>
