diff --git a/models/workflow/plantuml.go b/models/workflow/plantuml.go
index 9beaede..b1fe6e2 100644
--- a/models/workflow/plantuml.go
+++ b/models/workflow/plantuml.go
@@ -15,20 +15,52 @@ import (
 // PlantUML export
 // ---------------------------------------------------------------------------
 
-// ToPlantUML serializes the workflow graph back to a PlantUML file that is
-// compatible with ExtractFromPlantUML (round-trip).
-// Resource attributes and instance attributes are merged and written as
-// human-readable comments: "key: value, nested.key: value".
+// plantUMLProcedures defines the !procedure blocks for each resource type.
+// These make the output valid, renderable PlantUML while remaining parseable
+// by ExtractFromPlantUML (which already skips lines containing "!procedure").
+const plantUMLProcedures = `!procedure Processing($var, $name)
+  component "$name" as $var <<Processing>>
+!endprocedure
+
+!procedure Data($var, $name)
+  file "$name" as $var <<Data>>
+!endprocedure
+
+!procedure Storage($var, $name)
+  database "$name" as $var <<Storage>>
+!endprocedure
+
+!procedure ComputeUnit($var, $name)
+  node "$name" as $var <<ComputeUnit>>
+!endprocedure
+
+!procedure WorkflowEvent($var, $name)
+  usecase "$name" as $var <<WorkflowEvent>>
+!endprocedure
+
+!procedure Workflow($var, $name)
+  frame "$name" as $var <<Workflow>>
+!endprocedure
+`
+
+// ToPlantUML serializes the workflow graph to a valid, renderable PlantUML file
+// that is also compatible with ExtractFromPlantUML (round-trip).
+// Resource and instance attributes are written as human-readable comments:
+//
+//	Processing(p1, "NDVI") ' access.container.image: myrepo/ndvi:1.2, infrastructure: 0
 func (w *Workflow) ToPlantUML() string {
 	var sb strings.Builder
 	sb.WriteString("@startuml\n\n")
+	sb.WriteString(plantUMLProcedures)
+	sb.WriteByte('\n')
 
 	varNames := plantUMLVarNames(w.Graph.Items)
 
 	// --- resource declarations ---
 	for id, item := range w.Graph.Items {
-		sb.WriteString(plantUMLItemLine(varNames[id], item))
-		sb.WriteByte('\n')
+		if line := plantUMLItemLine(varNames[id], item); line != "" {
+			sb.WriteString(line + "\n")
+		}
 	}
 
 	sb.WriteByte('\n')