Refactor graph database types section for clarity and conciseness. Clarify description of ArcadeDB as a property graph database (#331)

Author: tae898

src/main/asciidoc/core-concepts/graphs.adoc

@@ -44,20 +44,18 @@ with:
 [discrete]
 ==== Graph Database Types
 
-There are two common types of graph databases,
-which are instances of directed graphs,
-but differ by the underlying objects of vertices and edges:
+There are two prevalent data models for graph databases (both usually directed):
 
-1. **Knowledge Graph**: the underlying vertex and edge objects are (just) labels.
-2. **Property Graph**: the underlying vertex and edge objects are (labeled) documents.
+1. **Triple store (RDF graph)**: data is represented as subject–predicate–object triples; all facts are uniform triples and semantics are standardized (RDF, RDFS/OWL, SPARQL).
+2. **Property Graph**: vertices and edges carry labels (types) and arbitrary key/value properties directly attached to them.
 
-ArcadeDB is a property graph, which means a vertex or edge consists of an identifier (RID),
-a label (type), and properties (document), in addition to the ordered pairs of endpoints.
-The latter are here vertex properties of incoming and outgoing edges, instead of edge properties of ordered vertex pairs, for technical reasons.
+ArcadeDB is a property graph database: vertices and edges have labels and can store arbitrary key/value properties, supporting compact storage, fast traversals, and flexible schema evolution within its multi-model, document‑oriented engine.
+
+Practically, a vertex or edge consists of an identifier (RID), a label (type), and properties (document), plus ordered endpoint references. The latter are here vertex properties of incoming and outgoing edges, instead of edge properties of ordered vertex pairs, for technical reasons.
 
 [discrete]
 ==== Why (Property) Graph Databases?
 
 - The modeled domain is already a network.
 - Fast traversal of relations instead of costly joins in relational databases.
-- Naturally annotated edges instead of inconvenient reification in knowledge graphs.
+- Naturally annotated edges instead of inconvenient reification in RDF graphs.