[cgrand-net]

No, it's hierarchical (because we nest collection types) vs relational.

[lincpa]

In RMDB(For example postgresql), Database is hierarchical nest collection types. It is also consistent with Clojure.

```clojure

{:table01 {:row01 {:col-array [0 1 2]

                   :col-json  "{\"a\": \"Hello\"}"

                   :col-text  "abc"}

           :row02 {}}
 
  :table02 {:row01 {}

            :row02 {}}}

```

In addition, postgresql supports inheritance, which is also hierarchical nest collection types.

[weavejester]

While Postgres supports hierarchical data in the form of JSON, that doesn't mean it's a form of relational data, it just means Postgres supports both.

Clojure doesn't have good tools in its core library for working with relational data. There's no core type that explicitly represents a relation, and Clojure lacks functions for many basic relational algebra operations. For example, how would you perform a natural join across your data structure?

[lincpa]

In programming, data modeling is the most important.

Convert(or design) data to hash-map, join (or merge) by key.

it can write commonly used operations as functions, try to row (or col) operations as much as possible, and join all data only when necessary(reduce the row-join).

```clojure

(def a {:a-id-01 {:a-name "a1"}

        :a-id-02 {:a-name "a2"}})

(def b {:b-id-01 {:a-id :a-id-01 :b-name "b2"}

        :b-id-02 {:a-id :a-id-02 :b-name "b2"}})

(->> b

     :b-id-01

     :a-id

     a

     :a-name)

;=>

;"a1"

(let [x (b :b-id-01)]

   (->> x  

        :a-id

        a

        (merge x ,)))

;=>

;{:a-id :a-id-01,

; :b-name "b2",

; :a-name "a1"}

```

[weavejester]

You're describing a language whose data model is hierarchical, not relational. In your code you first convert a relation into a hierarchy of collections. Why would you need to do that if Clojure used a relational data model?

[lincpa]

In RMDB, database data model (db,table, row, col, value[array,json, int, text, etc.] ) is hierarchical.

Relation is a logical model mapping of data structures, it is just a logical thinking that exists in the brain.

SQL, Prolog, clojure.core, minikanren can be used for relational operations.

[weavejester]

The relational model isn't arbitrarily hierarchical. We can place a map inside a map, or a map inside a vector, and keep going indefinitely until we run out of memory. Conversely, in a relational database we can't place a database into a table, or a table into a row.

It's true that we can represent relations using collections. In Clojure we'd write:

    (def a
      #{{:a/id 1, :a/name "a1"}
        {:a/id 2, :a/name "a2"}}

    (def b
      #{{:b/id 1, :b/name "b1", :a/id 2}}

But these structures don't allow for efficient lookup or joins, and we lack inbuilt functions to easily deal with data modelled in this way.

Relational databases are based on relational algebra. If Clojure is based on relational databases, then we'd expect to be able to do relational algebra easily in Clojure. But we can't: the core library isn't designed for it, and the built-in data structures aren't designed for it.