Add SPDX Java library family diagram

Add a diagram showing a family of SPDX Java libraries and their relationships to help implementers quickly get the overview.

The diagram is rendered from a PlantUML file.

Signed-off-by: Arthit Suriyawongkul <[email protected]>

Author: bact

README.md

@@ -50,6 +50,8 @@ See [README-V3-UPGRADE.md](README-V3-UPGRADE.md) for library upgrade instruction
 
 ## API Documentation
 
+[![SPDX Java library family diagram](spdx_java_lib_family.png)](./spdx_java_lib_family.png)
+
 Here are links to the API documentation for the family of SPDX Java libraries.
 
 "release" points to the API documentation of the latest stable version of the library, while "dev" points to the API documentation generated every time there is an update in the library's GitHub repository.

spdx_java_lib_family.plantuml

@@ -0,0 +1,65 @@
+' SPDX-FileCopyrightText: 2025 SPDX contributors
+' SPDX-FileType: DOCUMENTATION
+' SPDX-License-Identifier: Apache-2.0
+
+@startuml spdx_java_lib_family
+scale 1.5
+
+title Family of SPDX Java libraries
+
+' Left-to-right layout is more familiar for readers of left-to-right languages.
+left to right direction
+
+' Use "package" to group related components and improve readability.
+' This does not imply actual Java package structure.
+package "SPDX Java libraries" {
+    package "Core libraries" {
+        component "<b>java-spdx-library</b>\n(core library & helpers)" as lib #LightGreen
+        component "spdx-java-core\n(core utilities)" as core #LightYellow
+        interface "IModelStore\n(storage service provider interface)" as storeSPI #LightYellow
+    }
+
+    package "Models" {
+        component "spdx-java-model-2_X\n(SPDX 2 model)" as model2
+        component "spdx-java-model-3_0\n(SPDX 3 model)" as model3
+    }
+
+    package "Storage implementations" {
+        component "spdx-java-tagvalue-store\n(Tag-Value store)" as tagvalue
+        component "spdx-java-rdf-store\n(RDF store)" as rdf
+        component "spdx-java-spreadsheet-store\n(XLS spreadsheet store)" as sheet
+        component "spdx-java-jackson-store\n(JSON / YAML / XML store)" as jackson
+        component "spdx-java-v3jsonld-store\n(v3 JSON-LD store)" as v3jsonld
+    }
+
+    package "Tooling" {
+        component "spdx-model-to-java\n(code generator for SPDX 3 model)" as genmodel3
+        component "tools-java\n(command-line tools)" as tools
+        component "spdx-maven-plugin\n(Maven integration)" as maven
+    }
+
+    package "Specifications" {
+        component "SPDX 3 specification Turtle file" as spdx3turtle
+    }
+}
+
+' Core relationships
+lib --> core : depends on
+lib --> model2 : depends on
+lib --> model3 : depends on
+
+' Storage SPI and implementations
+core --> storeSPI : contains
+jackson ..|> storeSPI : implements
+rdf ..|> storeSPI : implements
+sheet ..|> storeSPI : implements
+tagvalue ..|> storeSPI : implements
+v3jsonld ..|> storeSPI : implements
+
+' Tooling
+maven --> lib : depends on
+tools --> lib : depends on
+genmodel3 --> model3 : generates
+genmodel3 --> spdx3turtle : depends on
+
+@enduml