diff --git a/packages/utils/dag.js b/packages/utils/dag.js
index 22369b4..d85ce64 100644
--- a/packages/utils/dag.js
+++ b/packages/utils/dag.js
@@ -1,7 +1,18 @@
 export default class DAG {
   constructor(nodes) {
     this.nodes = new Map(nodes.map((node) => [node._id, node]))
-    this.edges = []
+    this.edges = new Set()
+  }
+
+  format() {
+    this.nodes.forEach((_, id) => {
+      this.setLayer(id)
+      this.addEdges(id)
+    })
+  }
+
+  get(id) {
+    return this.nodes.get(id)
   }
 
   setLayer(id) {
@@ -18,13 +29,13 @@ export default class DAG {
     return node.layer
   }
 
-  format() {
-    this.nodes.forEach((_, id) => {
-      this.setLayer(id)
+  addEdges(id) {
+    const node = this.nodes.get(id)
+    if (!node) {
+      throw new Error(`Node ${id} not found`)
+    }
+    node.requirements.forEach((rId) => {
+      this.edges.add([rId, id])
     })
   }
-
-  get(id) {
-    return this.nodes.get(id)
-  }
 }
diff --git a/packages/utils/dag.test.js b/packages/utils/dag.test.js
index 272eeea..7dd3398 100644
--- a/packages/utils/dag.test.js
+++ b/packages/utils/dag.test.js
@@ -1,50 +1,133 @@
 import DAG from './dag.js'
 
-describe('dag', () => {
-  const data = [
-    {
-      _id: 'helloworld',
-      title: 'Hello, Linux World!',
-      requirements: [],
-    },
-    {
-      _id: 'spell',
-      title: 'Learn to spell',
-      requirements: ['helloworld'],
-    },
-    {
-      _id: 'discover',
-      title: 'Discover the World!',
-      requirements: ['spell'],
-    },
-    {
-      _id: 'read',
-      title: 'Read the File',
-      requirements: ['spell'],
-    },
-    {
-      _id: 'remove',
-      requirements: ['read', 'discover'],
-    },
-    {
-      _id: 'move',
-      requirements: ['helloworld'],
-    },
-    {
-      _id: 'copy',
-      requirements: ['remove', 'move'],
-    },
-  ]
-
-  it('should set layers', () => {
+describe('dag layers', () => {
+  it('two layer', () => {
+    const data = [
+      {
+        _id: 'helloworld',
+        requirements: [],
+      },
+      {
+        _id: 'spell',
+        requirements: ['helloworld'],
+      },
+    ]
     const dag = new DAG(data)
     dag.format()
     expect(dag.get('helloworld').layer).toBe(1)
     expect(dag.get('spell').layer).toBe(2)
-    expect(dag.get('move').layer).toBe(2)
-    expect(dag.get('read').layer).toBe(3)
-    expect(dag.get('discover').layer).toBe(3)
-    expect(dag.get('remove').layer).toBe(4)
-    expect(dag.get('copy').layer).toBe(5)
+  })
+  it('branch', () => {
+    const data = [
+      {
+        _id: 'helloworld',
+        requirements: [],
+      },
+      {
+        _id: 'spell',
+        requirements: ['helloworld'],
+      },
+      {
+        _id: 'discover',
+        requirements: ['helloworld'],
+      },
+    ]
+    const dag = new DAG(data)
+    dag.format()
+    expect(dag.get('helloworld').layer).toBe(1)
+    expect(dag.get('spell').layer).toBe(2)
+    expect(dag.get('discover').layer).toBe(2)
+  })
+  it('merge', () => {
+    const data = [
+      {
+        _id: 'A',
+        requirements: [],
+      },
+      {
+        _id: 'B',
+        requirements: [],
+      },
+      {
+        _id: 'C',
+        requirements: ['A', 'B'],
+      },
+    ]
+    const dag = new DAG(data)
+    dag.format()
+    expect(dag.get('A').layer).toBe(1)
+    expect(dag.get('B').layer).toBe(1)
+    expect(dag.get('C').layer).toBe(2)
+  })
+  it('skip', () => {
+    const data = [
+      {
+        _id: 'A',
+        requirements: [],
+      },
+      {
+        _id: 'B',
+        requirements: [],
+      },
+      {
+        _id: 'C',
+        requirements: ['A'],
+      },
+      {
+        _id: 'D',
+        requirements: ['B', 'C'],
+      },
+    ]
+    const dag = new DAG(data)
+    dag.format()
+    expect(dag.get('A').layer).toBe(1)
+    expect(dag.get('B').layer).toBe(1)
+    expect(dag.get('C').layer).toBe(2)
+    expect(dag.get('D').layer).toBe(3)
+  })
+})
+
+describe('dag edges', () => {
+  it('one edge', () => {
+    const data = [
+      {
+        _id: 'helloworld',
+        requirements: [],
+      },
+      {
+        _id: 'spell',
+        requirements: ['helloworld'],
+      },
+    ]
+
+    const dag = new DAG(data)
+    dag.format()
+    expect(dag.edges).toEqual(new Set([['helloworld', 'spell']]))
+  })
+
+  it('branch edges', () => {
+    const data = [
+      {
+        _id: 'helloworld',
+        requirements: [],
+      },
+      {
+        _id: 'spell',
+        requirements: ['helloworld'],
+      },
+      {
+        _id: 'discover',
+        requirements: ['helloworld'],
+      },
+    ]
+
+    const dag = new DAG(data)
+    dag.format()
+    expect(dag.edges).toEqual(
+      new Set([
+        ['helloworld', 'discover'],
+        ['helloworld', 'spell'],
+      ])
+    )
   })
 })