diff --git a/__init__.py b/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/compute.py b/compute.py
new file mode 100644
index 00000000..cf47183b
--- /dev/null
+++ b/compute.py
@@ -0,0 +1,41 @@
+
+import processGraph as pg
+
+import os
+import sys
+
+import argparse
+
+
+parser = argparse.ArgumentParser(description='Execute a Graph of processes.')
+parser.add_argument('graphFile', metavar='GRAPHFILE.mg', type=str,
+                    help='Filepath to a graph file.')
+parser.add_argument('--node', metavar='NODE_NAME', type=str,
+                    help='Process the node alone.')
+parser.add_argument('--graph', metavar='NODE_NAME', type=str,
+                    help='Process the node and all previous nodes needed.')
+parser.add_argument("--force", help="Force recompute",
+                    action="store_true")
+
+args = parser.parse_args()
+
+# graph = pg.Graph('bashTest')
+# ls = graph.addNewNode('Ls', input='/tmp')
+# appendText = graph.addNewNode('AppendText', inputText='plop')
+# graph.addEdge(ls.output, appendText.input)
+## graph.save(args.graphFile)
+
+graph = pg.loadGraph(args.graphFile)
+graph.update()
+
+if args.node:
+    # Execute the node
+    node = graph.nodes[args.node]
+    if args.force or node.status.status != pg.Status.SUCCESS:
+        node.process()
+else:
+    startNodes = None
+    if args.graph:
+        startNodes = [graph.nodes[args.graph]]
+    pg.execute(graph, startNodes=startNodes, force=args.force)
+
diff --git a/newNodeType.py b/newNodeType.py
new file mode 100644
index 00000000..bff941b8
--- /dev/null
+++ b/newNodeType.py
@@ -0,0 +1,55 @@
+
+import processGraph as pg
+
+import os
+import sys
+import re
+import argparse
+
+
+parser = argparse.ArgumentParser(description='Create a new Node Type')
+parser.add_argument('node', metavar='NodeName', type=str,
+                    help='New node name')
+
+args = parser.parse_args()
+
+if sys.stdin.isatty():
+    print('No input documentation.')
+    print('Usage: YOUR_COMMAND --help | {cmd} YourCommand'.format(cmd=os.path.splitext(__file__)[0]))
+    exit(-1)
+
+inputDoc = [line for line in sys.stdin]
+inputArgs = [line for line in inputDoc if '--' in line]
+
+arg_re = re.compile('.*?--(?P<longName>\w+).*?')
+
+
+def convertToLabel(name):
+    camelCaseToLabel = re.sub('(.)([A-Z][a-z]+)', r'\1 \2', name)
+    snakeToLabel = ' '.join(word.capitalize() for word in camelCaseToLabel.split('_'))
+    snakeToLabel = ' '.join(word.capitalize() for word in snakeToLabel.split(' '))
+    # print name, camelCaseToLabel, snakeToLabel
+    return snakeToLabel
+
+
+outputNodeStr = '''
+import processGraph as pg
+
+class __COMMANDNAME__(pg.CommandLineNodeDesc):
+    internalFolder = '{nodeType}/{uid0}/'
+    cmdLineExpr = '{nodeType} {allParams}'
+'''.replace('__COMMANDNAME__', 'args.node')
+
+for inputArg in inputArgs:
+    paramName = arg_re.match(inputArg).group('longName')
+
+    inputArgLower = inputArg.lower()
+    isFile = 'path' in inputArgLower or 'folder' in inputArgLower or 'file' in inputArgLower
+    outputNodeStr += '''
+    {name} = pg.{attributeType}(
+            label='{label}',
+            uid=[0],
+            )'''.format(name=paramName, label=convertToLabel(paramName), attributeType='FileAttribute' if isFile else 'ParamAttribute')
+
+
+print(outputNodeStr)
\ No newline at end of file
diff --git a/nodes/AppendText.py b/nodes/AppendText.py
new file mode 100644
index 00000000..17c353a2
--- /dev/null
+++ b/nodes/AppendText.py
@@ -0,0 +1,19 @@
+from processGraph import desc
+
+class AppendText(desc.CommandLineNode):
+    commandLine = 'cat {inputValue} > {outputValue} && echo {inputTextValue} >> {outputValue}'
+    input = desc.FileAttribute(
+        label='Input File',
+        uid=[0],
+        )
+    output = desc.FileAttribute(
+        label='Output',
+        value='{cache}/{nodeType}/{uid0}/appendText.txt',
+        isOutput=True,
+        hasExpression=True,
+        )
+    inputText = desc.FileAttribute(
+        label='Input Text',
+        uid=[0],
+        )
+
diff --git a/nodes/Ls.py b/nodes/Ls.py
new file mode 100644
index 00000000..c3fd339f
--- /dev/null
+++ b/nodes/Ls.py
@@ -0,0 +1,16 @@
+from processGraph import desc
+
+
+class Ls(desc.CommandLineNode):
+    commandLine = 'ls {inputValue} > {outputValue}'
+    input = desc.FileAttribute(
+        label='Input',
+        uid=[0],
+        )
+    output = desc.FileAttribute(
+        label='Output',
+        value='{cache}/{nodeType}/{uid0}/ls.txt',
+        isOutput=True,
+        hasExpression=True,
+        )
+
diff --git a/nodes/__init__.py b/nodes/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/processGraph/Graph.py b/processGraph/Graph.py
new file mode 100644
index 00000000..9b3bb2e7
--- /dev/null
+++ b/processGraph/Graph.py
@@ -0,0 +1,604 @@
+from __future__ import print_function
+
+import processGraph as pg
+
+from collections import defaultdict
+import psutil
+import inspect
+from pprint import pprint
+import json
+
+# Replace default encoder to support Enums
+DefaultJSONEncoder = json.JSONEncoder # store the original one
+class MyJSONEncoder(DefaultJSONEncoder): # declare a new one with Enum support
+    def default(self, obj):
+        if isinstance(obj, Enum):
+            return obj.name
+        return DefaultJSONEncoder.default(self, obj) # use the default one for all other types
+json.JSONEncoder = MyJSONEncoder # replace the default implementation with our new one
+
+import time
+import os
+import uuid
+
+import threading
+import subprocess
+import hashlib
+
+from enum import Enum # available by default in python3. For python2: "pip install enum34"
+
+
+try:
+    unicode = unicode
+except NameError:
+    # 'unicode' is undefined, must be Python 3
+    str = str
+    unicode = str
+    bytes = bytes
+    basestring = (str, bytes)
+else:
+    # 'unicode' exists, must be Python 2
+    str = str
+    unicode = unicode
+    bytes = str
+    basestring = basestring
+
+
+def hash(v):
+    hashObject = hashlib.sha1(str(v).encode('utf-8'))
+    return hashObject.hexdigest()
+
+
+class Attribute:
+    '''
+    '''
+    def __init__(self, name, node, attributeDesc):
+        self.attrName = name
+        self.node = node
+        self._value = attributeDesc.__dict__.get('value', None)
+        self.attributeDesc = attributeDesc
+
+    def aboluteName(self):
+        return '{}.{}.{}'.format(self.node.graph.name, self.node.name, self.attrName)
+
+    def name(self):
+        '''
+        Name inside the Graph.
+        '''
+        return '{}.{}'.format(self.node.name, self.attrName)
+
+    def uid(self):
+        '''
+        '''
+        if self.attributeDesc.isOutput:
+            # only dependent of the linked node uid, so it is independant of the cache folder which may be used in the filepath.
+            return self.node.uid()
+        if self.isLink():
+            return self.node.graph.edges[self].uid()
+        if isinstance(self._value, basestring):
+            return hash(str(self._value))
+        return hash(self._value)
+
+    def isLink(self):
+        '''
+        If the attribute is a link to another attribute.
+        '''
+        if self.attributeDesc.isOutput:
+            return False
+        else:
+            return self in self.node.graph.edges
+
+    def getLinkParam(self):
+        if not self.isLink():
+            return None
+        return self.node.graph.edges[self]
+
+    def _applyExpr(self):
+        '''
+        For string parameters with an expression (when loaded from file),
+        this function convert the expression into a real edge in the graph
+        and clear the string value.
+        '''
+        v = self._value
+        if isinstance(v, basestring) and len(v) > 2 and v[0] == '{' and v[-1] == '}':
+            # value is a link to another attribute
+            g = self.node.graph
+            link = v[1:-1]
+            linkNode, linkAttr = link.split('.')
+            g.addEdge(g.nodes[linkNode].attributes[linkAttr], self)
+            self._value = ""
+
+    def getExportValue(self):
+        value = self._value
+        # print('getExportValue: ', self.name(), value, self.isLink())
+        if self.isLink():
+            value = '{' + self.node.graph.edges[self].name() + '}'
+        return value
+
+
+class Status(Enum):
+    '''
+    '''
+    NONE = 1
+    SUBMITTED_EXTERN = 2
+    SUBMITTED_LOCAL = 3
+    RUNNING = 4
+    ERROR = 5
+    SUCCESS = 6
+
+
+class Statistics:
+    '''
+    '''
+    def __init__(self):
+        self.duration = 0 # computation time set at the end of the execution
+        self.cpuUsage = []
+        self.nbCores = 0
+        self.cpuFreq = 0
+        self.ramUsage = [] # store cpuUsage every minute
+        self.ramAvailable = 0 # GB
+        self.vramUsage = []
+        self.vramAvailable = 0 # GB
+        self.swapUsage = []
+        self.swapAvailable = 0
+    def toDict(self):
+        return self.__dict__
+    def fromDict(self, d):
+        self.__dict__ = d
+
+
+class StatusData:
+    '''
+    '''
+    def __init__(self, nodeName, nodeType):
+        self.status = Status.NONE
+        self.nodeName = nodeName
+        self.nodeType = nodeType
+        self.statistics = Statistics()
+        self.graph = ''
+
+    def toDict(self):
+        return {k: (v.toDict() if getattr(v, "toDict", None) else v) for k, v in self.__dict__.items()}
+
+    def fromDict(self, d):
+        self.status = Status._member_map_[d['status']]
+        self.nodeName = d['nodeName']
+        self.nodeType = d['nodeType']
+        self.statistics.fromDict(d['statistics'])
+        self.graph = d['graph']
+
+
+bytesPerGiga = 1024.*1024.*1024.
+
+class StatisticsThread(threading.Thread):
+ 
+    def __init__(self, node):
+        threading.Thread.__init__(self)
+        self.node = node
+        self.running = True
+        self.statistics = self.node.status.statistics
+        self.initStats()
+
+    def initStats(self):
+        self.lastTime = time.time()
+        self.statistics.duration = 0
+        self.statistics.cpuUsage = []
+        self.statistics.nbCores = psutil.cpu_count(logical=False)
+        self.statistics.cpuFreq = psutil.cpu_freq()[2]
+        self.statistics.ramUsage = []
+        self.statistics.ramAvailable = psutil.virtual_memory().total / bytesPerGiga
+        self.statistics.swapUsage = []
+        self.statistics.swapAvailable = psutil.swap_memory().total / bytesPerGiga
+        self.statistics.vramUsage = []
+        self.statistics.vramAvailable = 0
+        self.updateStats()
+
+    def updateStats(self):
+        self.lastTime = time.time()
+        self.statistics.cpuUsage.append(psutil.cpu_percent(interval=0.1, percpu=True))
+        self.statistics.ramUsage.append(psutil.virtual_memory().percent)
+        self.statistics.swapUsage.append(psutil.swap_memory().percent)
+        self.statistics.vramUsage.append(0)
+        self.node.saveStatusFile()
+
+    def run(self):
+        while self.running:
+            if time.time() - self.lastTime > 10:
+                self.updateStats()
+            time.sleep(1)
+ 
+
+class Node:
+    '''
+    '''
+    name = None
+    graph = None
+    
+
+    def __init__(self, nodeDesc, **kwargs):
+        self.nodeDesc = pg.nodesDesc[nodeDesc]()
+        self.attributes = {}
+        self.attributesPerUid = defaultdict(set)
+        self._initFromDesc()
+        for k, v in kwargs.items():
+            self.attributes[k]._value = v
+        self.status = StatusData(self.name, self.nodeType())
+
+    def __getattr__(self, k):
+        try:
+            # Throws exception if not in prototype chain
+            # return object.__getattribute__(self, k) # doesn't work in python2
+            return object.__getattr__(self, k)
+        except AttributeError:
+            try:
+                return self.attributes[k]
+            except KeyError:
+                raise AttributeError(k)
+
+    def _initFromDesc(self):
+        # Init from class members
+        for name, desc in self.nodeDesc.__class__.__dict__.items():
+            if issubclass(desc.__class__, pg.desc.Attribute):
+                self.attributes[name] = Attribute(name, self, desc)
+        # Init from instance members
+        for name, desc in self.nodeDesc.__dict__.items():
+            if issubclass(desc.__class__, pg.desc.Attribute):
+                self.attributes[name] = Attribute(name, self, desc)
+        # List attributes per uid
+        for name, attr in self.attributes.items():
+            for uidIndex in attr.attributeDesc.uid:
+                self.attributesPerUid[uidIndex].add(attr)
+
+    def _applyExpr(self):
+        for attr in self.attributes.values():
+            attr._applyExpr()
+
+    def nodeType(self):
+        return self.nodeDesc.__class__.__name__
+
+    def uid(self):
+        return self.nodeUid
+
+    def _updateUid(self):
+        hashInputParams = [(attr.attrName, attr.uid()) for attr in self.attributes.values() if not attr.attributeDesc.isOutput]
+        hashInputParams.sort()
+        self.nodeUid = hash(tuple([b for a, b in hashInputParams]))
+        return self.nodeUid
+
+    def getDepth(self):
+        return self.graph.getDepth(self)
+
+    def toDict(self):
+        attributes = {k: v.getExportValue() for k, v in self.attributes.items()}
+        return {
+            'nodeType': self.nodeType(),
+            'attributes': {k: v for k, v in attributes.items() if v is not None}, # filter empty values
+            }
+
+    def updateInternals(self):
+        self._updateUid()
+
+        self._cmdVars = {}
+        for uidIndex, associatedAttributes in self.attributesPerUid.items():
+            assAttr = [(a.attrName, a.uid()) for a in associatedAttributes]
+            assAttr.sort()
+            self._cmdVars['uid{}'.format(uidIndex)] = hash(tuple([b for a, b in assAttr]))
+
+        for name, attr in self.attributes.items():
+            if attr.attributeDesc.isOutput:
+                attr._value = attr.attributeDesc.value.format(
+                    cache=pg.cacheFolder,
+                    nodeType=self.nodeType(),
+                    **self._cmdVars) # self._cmdVars only contains uids at this step
+
+        for name, attr in self.attributes.items():
+            linkAttr = attr.getLinkParam()
+            v = attr._value
+            if linkAttr:
+                v = linkAttr._value 
+
+            self._cmdVars[name] = '--{name} {value}'.format(name=name, value=v)
+            self._cmdVars[name + 'Value'] = str(v)
+            self._cmdVars[attr.attributeDesc.group] = self._cmdVars.get(attr.attributeDesc.group, '') + ' ' + self._cmdVars[name]
+
+    def internalFolder(self):
+        return self.nodeDesc.internalFolder.format(nodeType=self.nodeType(), **self._cmdVars)
+
+    def commandLine(self):
+        return self.nodeDesc.commandLine.format(nodeType=self.nodeType(), **self._cmdVars)
+
+    def statusFile(self):
+        return os.path.join(pg.cacheFolder, self.internalFolder(), 'status')
+
+    def logFile(self):
+        return os.path.join(pg.cacheFolder, self.internalFolder(), 'log')
+
+    def updateStatusFromCache(self):
+        '''
+        Need up-to-date UIDs.
+        '''
+        statusFile = self.statusFile()
+        if not os.path.exists(statusFile):
+            self.status.status = Status.NONE
+            return
+        with open(statusFile, 'r') as jsonFile:
+            statusData = json.load(jsonFile)
+        self.status.fromDict(statusData)
+
+    def saveStatusFile(self):
+        '''
+        Need up-to-date UIDs.
+        '''
+        data = self.status.toDict()
+        statusFilepath = self.statusFile()
+        folder = os.path.dirname(statusFilepath)
+        if not os.path.exists(folder):
+            os.makedirs(folder)
+        statusFilepathWriting = statusFilepath + '.writing.' + str(uuid.uuid4())
+        with open(statusFilepathWriting, 'w') as jsonFile:
+            json.dump(data, jsonFile, indent=4)
+        os.rename(statusFilepathWriting, statusFilepath)
+
+    def upgradeStatusTo(self, newStatus):
+        if int(newStatus.value) <= int(self.status.status.value):
+            print('WARNING: downgrade status on node "{}" from {} to {}'.format(self.name, self.status.status.name, newStatus))
+        self.status.status = newStatus
+        self.saveStatusFile()
+
+    def submit(self):
+        self.upgradeStatusTo(pg.Status.SUBMITTED_EXTERN)
+
+    def beginSequence(self):
+        self.upgradeStatusTo(pg.Status.SUBMITTED_LOCAL)
+        
+    def process(self):
+        self.upgradeStatusTo(pg.Status.RUNNING)
+        statThread = StatisticsThread(self)
+        statThread.start()
+        try:
+            with open(self.logFile(), 'w') as logF:
+                cmd = self.commandLine()
+                print(' =====> commandLine: ', cmd)
+                print(' - logFile: ', self.logFile())
+                subprocess.call(cmd, stdout=logF, stderr=logF, shell=True)
+        except:
+            self.upgradeStatusTo(pg.Status.ERROR)
+            raise
+        statThread.running = False
+        statThread.join()
+
+        self.upgradeStatusTo(pg.Status.SUCCESS)
+        
+    def endSequence(self):
+        pass
+
+WHITE = 0
+GRAY = 1
+BLACK = 2
+
+class Visitor:
+    # def initializeVertex(self, s, g):
+    #     '''is invoked on every vertex of the graph before the start of the graph search.'''
+    #     pass
+    # def startVertex(self, s, g):
+    #     '''is invoked on the source vertex once before the start of the search.'''
+    #     pass
+    def discoverVertex(self, u, g):
+        '''is invoked when a vertex is encountered for the first time.'''
+        pass
+    # def examineEdge(self, e, g):
+    #     '''is invoked on every out-edge of each vertex after it is discovered.'''
+    #     pass
+    # def treeEdge(self, e, g):
+    #     '''is invoked on each edge as it becomes a member of the edges that form the search tree. If you wish to record predecessors, do so at this event point.'''
+    #     pass
+    # def backEdge(self, e, g):
+    #     '''is invoked on the back edges in the graph.'''
+    #     pass
+    # def forwardOrCrossEdge(self, e, g):
+    #     '''is invoked on forward or cross edges in the graph. In an undirected graph this method is never called.'''
+    #     pass
+    # def finishEdge(self, e, g):
+    #     '''is invoked on the non-tree edges in the graph as well as on each tree edge after its target vertex is finished.'''
+    #     pass
+    def finishVertex(self, u, g):
+        '''is invoked on a vertex after all of its out edges have been added to the search tree and all of the adjacent vertices have been discovered (but before their out-edges have been examined).'''
+        pass
+
+
+class Graph:
+    '''
+    _________________      _________________      _________________
+    |               |      |               |      |               |
+    |     Node A    |      |     Node B    |      |     Node C    |
+    |               | edge |               | edge |               |
+    |input    output|>---->|input    output|>---->|input    output|
+    |_______________|      |_______________|      |_______________|
+
+    Data structures:
+
+        nodes = {'A': <nodeA>, 'B': <nodeB>, 'C': <nodeC>}
+        edges = {B.input: A.output, C.input: B.output,}
+
+
+    '''
+    def __init__(self, name):
+        self.name = name
+        self.nodes = {}
+        self.edges = {} # key/input <- value/output, it is organized this way because key/input can have only one connection.
+
+    def addNode(self, node, uniqueName=None):
+        if node.graph != None and node.graph != self:
+            raise RuntimeError('Node "{}" cannot be part of the Graph "{}", as it is already part of the other graph "{}".'.format(
+                self.node.nodeType(), self.name, node.graph.name))
+        if uniqueName:
+            assert(uniqueName not in self.nodes)
+            node.name = uniqueName
+        else:
+            node.name = self._createUniqueNodeName(node.nodeType())
+        node.graph = self
+        self.nodes[node.name] = node
+
+        return node
+
+    def addNewNode(self, nodeName, *args, **kwargs):
+        return self.addNode(Node(nodeDesc=nodeName, *args, **kwargs))
+
+    def _createUniqueNodeName(self, inputName):
+        i = 1
+        while i:
+            newName = "{name}_{index}".format(name=inputName, index=i)
+            if newName not in self.nodes:
+                return newName
+            i += 1
+
+    def getLeaves(self):
+        nodesWithOuput = set([outputAttr.node for outputAttr in self.edges.values()])
+        return set(self.nodes.values()) - nodesWithOuput
+
+    def addEdge(self, outputAttr, inputAttr):
+        assert(isinstance(outputAttr, Attribute))
+        assert(isinstance(inputAttr, Attribute))
+        if(outputAttr.node.graph != self or inputAttr.node.graph != self):
+            raise RuntimeError('The attributes of the edge should be part of a common graph.')
+        if inputAttr in self.edges:
+            raise RuntimeError('Input attribute "{}" is already connected.'.format(inputAttr.fullName()))
+        self.edges[inputAttr] = outputAttr
+
+    def addEdges(self, *edges):
+        for edge in edges:
+            self.addEdge(*edge)
+
+    def getDepth(self, node):
+        return len(self.dfsNodesOnFinish([node]))
+
+    def _getNodeEdges(self):
+        nodeEdges = defaultdict(set)
+
+        for attrInput, attrOutput in self.edges.items():
+            nodeEdges[attrInput.node].add(attrOutput.node)
+
+        return nodeEdges
+
+    def dfs(self, visitor, startNodes=None):
+        nodeChildrens = self._getNodeEdges()
+        colors = {}
+        for u in self.nodes.values():
+            colors[u] = WHITE
+        time = 0
+        if startNodes:
+            for startNode in startNodes:
+                self.dfsVisit(startNode, visitor, colors, nodeChildrens)
+        else:
+            leaves = self.getLeaves()
+            for u in leaves:
+                if colors[u] == WHITE:
+                    self.dfsVisit(u, visitor, colors, nodeChildrens)
+
+    def dfsVisit(self, u, visitor, colors, nodeChildrens):
+        colors[u] = GRAY
+        visitor.discoverVertex(u, self)
+        # d_time[u] = time = time + 1
+        for v in nodeChildrens[u]:
+            if colors[v] == WHITE:
+                # (u,v) is a tree edge
+                self.dfsVisit(v, visitor, colors, nodeChildrens) # TODO: avoid recursion
+            elif colors[v] == GRAY:
+                pass # (u,v) is a back edge
+            elif colors[v] == BLACK:
+                pass # (u,v) is a cross or forward edge
+        colors[u] = BLACK
+        visitor.finishVertex(u, self)
+
+    def dfsNodesOnFinish(self, startNodes=None):
+        nodes = []
+        visitor = Visitor()
+        visitor.finishVertex = lambda vertex, graph: nodes.append(vertex)
+        self.dfs(visitor=visitor, startNodes=startNodes)
+        return nodes
+
+    def dfsNodesToProcess(self, startNodes=None):
+        nodes = []
+        visitor = Visitor()
+        def finishVertex(vertex, graph):
+            if vertex.status.status in (Status.SUBMITTED_EXTERN,
+                                        Status.SUBMITTED_LOCAL):
+                print('WARNING: node "{}" is already submitted.'.format(vertex.name))
+            if vertex.status.status is Status.RUNNING:
+                print('WARNING: node "{}" is already running.'.format(vertex.name))
+            if vertex.status.status is not Status.SUCCESS:
+                nodes.append(vertex)
+        visitor.finishVertex = finishVertex
+        self.dfs(visitor=visitor, startNodes=startNodes)
+        return nodes
+
+    def _applyExpr(self):
+        for node in self.nodes.values():
+            node._applyExpr()
+
+    def toDict(self):
+        return {k: node.toDict() for k, node in self.nodes.items()}
+
+    def save(self, filepath):
+        '''
+        '''
+        data = self.toDict()
+        pprint(data)
+        with open(filepath, 'w') as jsonFile:
+            json.dump(data, jsonFile, indent=4)
+
+    def updateInternals(self, startNodes=None):
+        nodes = self.dfsNodesOnFinish(startNodes=startNodes)
+        for node in nodes:
+            node.updateInternals()
+
+    def updateStatusFromCache(self):
+        for node in self.nodes.values():
+            node.updateStatusFromCache()
+
+    def update(self):
+        self.updateInternals()
+        self.updateStatusFromCache()
+
+
+def loadGraph(filepath):
+    '''
+    '''
+    graphData = None
+    with open(filepath) as jsonFile:
+        graphData = json.load(jsonFile)
+    if not isinstance(graphData, dict):
+        raise RuntimeError('loadGraph error: Graph is not a dict. File: {}'.format(filepath))
+
+    graph = Graph(os.path.splitext(os.path.basename(filepath))[0])
+    for nodeName, nodeData in graphData.items():
+        if not isinstance(nodeData, dict):
+            raise RuntimeError('loadGraph error: Node is not a dict. File: {}'.format(filepath))
+        n = Node(nodeData['nodeType'], **nodeData['attributes'])
+        graph.addNode(n, uniqueName=nodeName)
+    graph._applyExpr()
+    return graph
+
+
+def execute(graph, startNodes=None, force=False):
+    '''
+    '''
+    if force:
+        nodes = graph.dfsNodesOnFinish(startNodes=startNodes)
+    else:
+        nodes = graph.dfsNodesToProcess(startNodes=startNodes)
+
+    print('execute: ', str([n.name for n in nodes]))
+
+    for node in nodes:
+        node.updateInternals()
+
+    for node in nodes:
+        node.beginSequence()
+
+    for node in nodes:
+        node.process()
+
+    for node in nodes:
+        node.endSequence()
+
diff --git a/processGraph/__init__.py b/processGraph/__init__.py
new file mode 100644
index 00000000..02cb775a
--- /dev/null
+++ b/processGraph/__init__.py
@@ -0,0 +1,55 @@
+from .Graph import *
+from . import desc
+
+import os
+import sys
+import re
+import inspect
+import importlib
+import json
+
+cacheFolder = '/tmp/processGraphCache'
+nodesDesc = {}
+
+
+def loadNodesDesc(folder, package='nodes'):
+    '''
+    '''
+    global nodesDesc
+
+    pysearchre = re.compile('.py$', re.IGNORECASE)
+    pluginfiles = filter(pysearchre.search,
+                           os.listdir(os.path.join(folder,
+                                                 package)))
+    # import parent module
+    importlib.import_module(package)
+    nodeTypes = []
+    errors = []
+    for pluginFile in pluginfiles:
+        if pluginFile.startswith('__'):
+            continue
+
+        try:
+            pluginName = os.path.splitext(pluginFile)[0]
+            module = '.' + pluginName
+            m = importlib.import_module(module, package=package)
+            p = [a for a in m.__dict__.values() if inspect.isclass(a) and issubclass(a, desc.Node)]
+            if not p:
+                raise RuntimeError('No class defined in plugin: %s' % module)
+            nodeTypes.extend(p)
+        except Exception as e:
+            errors.append('  * Errors while loading "{}".\n    File: {}\n    {}'.format(pluginName, pluginFile, str(e)))
+
+
+    nodesDesc = dict([(m.__name__, m) for m in nodeTypes])
+    print('Plugins loaded: ', ', '.join(nodesDesc.keys()))
+    if errors:
+        print('== Error while loading the following plugins: ==')
+        print('\n'.join(errors))
+        print('================================================')
+
+    return nodeTypes
+
+# Load plugins
+loadNodesDesc(folder=os.path.dirname(os.path.dirname(__file__)))
+
diff --git a/processGraph/desc.py b/processGraph/desc.py
new file mode 100644
index 00000000..611d4e00
--- /dev/null
+++ b/processGraph/desc.py
@@ -0,0 +1,45 @@
+import inspect
+import os
+
+
+class Attribute:
+    '''
+    '''
+    isOutput = False
+    uid = []
+    group = 'allParams'
+    commandLine = '{nodeType} --help' # need to be overridden
+    def __init__(self):
+        pass
+
+
+class FileAttribute(Attribute):
+    '''
+    '''
+    def __init__(self, **kwargs):
+        for k, v in kwargs.items():
+            setattr(self, k, v)
+
+
+class ParamAttribute(Attribute):
+    '''
+    '''
+    def __init__(self, **kwargs):
+        for k, v in kwargs.items():
+            setattr(self, k, v)
+
+
+class Node:
+    '''
+    '''
+    internalFolder = '{nodeType}/{uid0}/'
+
+    def __init__(self):
+        pass
+
+
+class CommandLineNode(Node):
+    '''
+    '''
+    def __init__(self):
+        pass
diff --git a/tests/test_task.py b/tests/test_task.py
new file mode 100644
index 00000000..f66d6800
--- /dev/null
+++ b/tests/test_task.py
@@ -0,0 +1,23 @@
+import processGraph as pg
+from nose.tools import *
+
+
+def test_depth():
+    graph = pg.Graph('Tests tasks depth')
+
+    tA = graph.addNewNode('Ls', input='/tmp')
+    tB = graph.addNewNode('AppendText', inputText='echo B')
+    tC = graph.addNewNode('AppendText', inputText='echo C')
+
+    graph.addEdges(
+        (tA.output, tB.input),
+        (tB.output, tC.input)
+        )
+
+    assert_equal(tA.getDepth(), 1)
+    assert_equal(tB.getDepth(), 2)
+    assert_equal(tC.getDepth(), 3)
+
+
+if __name__ == '__main__':
+    test_depth()