First query of a datomic database - datomic

Question

I can access the repl and I have a uri that I can connect with. How do I connect, see what entities and attributes exist, and see their values then drill down and so on? I am just using the free version that I did not have to register for.
So far this is what I have tried:
C:\programs\datomic-free-0.9.5327>.\bin\repl
Clojure 1.6.0
user=> (use '[datomic.api :only [q db] :as d])
nil
user=> (def conn (d/connect "datomic:dev://localhost:4334/somedb"))
IllegalArgumentExceptionInfo :db.error/unsupported-protocol Unsupported protocol :dev datomic.error/arg (error.clj:57)
user=>
user=> (def conn (d/connect "datomic://localhost:4334/somedb"))
IllegalArgumentExceptionInfo :db.error/invalid-db-uri Invalid database URI datomic://localhost:4334/somedb datomic.error/arg (error.clj:57)
user=> (def conn (d/connect "datomic:mem//somedb"))
IllegalArgumentExceptionInfo :db.error/invalid-db-uri Invalid database URI datomic:mem//somedb datomic.error/arg (error.clj:57)
With a MySql or an Oracle database an operator is able (given the right password) to list all the databases, connect to one of them, see its tables, then start things rolling by querying one of them.
By way of context even though this database ('somedb') is 'in memory', I still do expect it to exist, because there is a transactor running. However the transactor is a bit suspicious because this is what it looks like:
C:\programs\datomic-free-0.9.5327>.\bin\transactor .\config\samples\free-transactor-template.properties
Starting datomic:free://localhost:4334/<DB-NAME>, storing data in: data ...
System started datomic:free://localhost:4334/<DB-NAME>, storing data in: data
I am confused about querying a database that is supposed to be up and running and have values in it.

Answer 1

I can clarify these errors:
user=> (use '[datomic.api :only [q db] :as d])
nil
user=> (def conn (d/connect "datomic:dev://localhost:4334/somedb"))
IllegalArgumentExceptionInfo :db.error/unsupported-protocol Unsupported protocol :dev datomic.error/arg (error.clj:57)
Here the URI is formatted correctly, but the error indicates you're trying to access a pro exclusive storage (dev) rather than the storages allowed by free (free and mem). Note that you can access pro storage formats with the free level starter license (i.e. you don't need a paid license to get going with it).
user=> (def conn (d/connect "datomic://localhost:4334/somedb"))
IllegalArgumentExceptionInfo :db.error/invalid-db-uri Invalid database URI datomic://localhost:4334/somedb datomic.error/arg (error.clj:57)
Here you're not specifying a storage protocol at all, i.e. where dev is in the first call. This is required.
user=> (def conn (d/connect "datomic:mem//somedb"))
IllegalArgumentExceptionInfo :db.error/invalid-db-uri Invalid database URI datomic:mem//somedb datomic.error/arg (error.clj:57)
Here you're missing the : after mem. For the above errors, the API documentation for connect covers correct URI construction.
You can list databases with get-database-names, documented here.
To get up and running with queries, you might have a better first experience using the console, a web app/GUI which handles this automatic listing of databases, connecting to one, querying, etc.