Structured Occurrence Network for provenance: talk for ipaw12 paper

Modelling provenance using
Structured Occurrence Networks

Paolo Missier, Brian Randell, Maciej Koutny
Newcastle University, UK

IPAW’12
Santa Barbara, CA, June 2012

Thursday, June 21, 2012

Petri Nets and Occurrence Nets

Historically, Occurrence Nets have been used to define
process semantics of Petri Nets [2]
IPAW 2012 - P.Missier

[2] Best, Eike, and Raymond Devillers. “Sequential and concurrent behaviour in Petri net theory.” Theoretical Computer
Science 55, no. 1 (1987): 87-136. http://www.sciencedirect.com/science/article/pii/0304397587900909.
2


Occurrence Nets

ON is about capturing causal relationships
between events and conditions

ON = (C, E, F ) with nodes C E and a ﬂow relation F ⊆ (C ×E)∪(E × C) satisfying the following:
(i) for every condition c there is at most one event e such that (e,c) ∈ F, and at most one event f such that (c,f) ∈ F;
(ii) for every event e there is at least one condition c such that (c, e) ∈ F , and at least one condition d such that (e,
d) ∈ F ;
(iii) ON forms an acyclic graph and F + is a partial order relation (the relation PrecON = (F ◦ F)|C×C is acyclic)

3


Provenance and Occurrence Nets
• "Provenance is defined as a record that • An Occurrence Net is an abstract record of
describes the people, institutions, a single execution of some computing
entities, and activities involved in system
producing, influencing, or delivering a • Only information about causality and
piece of data or a thing." [PROV] concurrency between events and visited
local states is represented

4



Data: The evolution of variable A as a ON:

4



Data: The evolution of variable A as a ON:

Agents: The evolution of Bob, the document editor:
read drafted ready
performed verified
ptd paper internal to
exp. results draft
p1 memo

read
paper
p2

4


From ON to Structured ON
ON is an adequate starting point, but extensions are needed to
represent the activity of complex systems

• Structured Occurrence Nets provide these extensions as new
relationships amongst multiple ONs [2]

[2] Koutny, M., and B Randell. “Structured Occurrence Nets: A Formalism for Aiding System Failure Prevention and
Analysis Techniques.” Fundamenta Informaticae 97 (2009).
5


Provenance modelling patterns using SON

Main goal of this work:
to explore the use of Structured Occurrence Nets
as a formal model of provenance

• Data is viewed as an evolving system

• Agents are also evolving systems, thus their evolution is also captured

• Uniform representation of Agents / Activity / Data interplay

• Representation of multi-layered Provenance
– eg:the provenance of a workflow run is underpinned by system-level provenance
– SONs are suitable for modelling at multiple levels of abstraction

Expected by-product of the investigation:
suggest enhancements to the current SON model
6


Talk outline
• C-SON: ON + communication relation
– a provenance pattern to represent workflow patterns

• T-SON: C-SON + temporal abstraction
• (more abstraction relations omitted in the talk)
• Modelling multi-layered provenance
• Agents as evolving systems
– provenance of agents

7


Communication SONs
• Goal: to capture communication between ONs that otherwise proceed
concurrently
• by introducing a Communication relation amongst activities in two ONs
– induces a partial order on the states and conditions of the two nets
– must result in an acyclic net

e1 cannot have happened after f1

e2, f2 must have happened simultaneously

8


C-SON at work - a first provenance pattern

• Each ON models one variable as a system.
• The composed activity “A:=A+1; A:=A+B; B:=A+B” is represented as a SON
composed of a pair of communicating ONs

• The resulting SON captures a (partial) order of possible reads and writes
leading to the final result

9


Workflow execution traces using C-SON

X= 10

Y:= f(X)
(a) (b)
Program Execution
specification instance f()

<X,Z> := g(X,Y) Y = "200"

g()

X = 20 Z = "20"

10 r 10 r 10 w 20

X

(c)
SON representation of
Execution trace f g

Program
execution

w 20
w 200 r 200
Z
Y

10


Temporal SON (T-SON)
• Goal: to replace part of an ON with new “atomic” actions
– a form of temporal abstraction
– these new actions only appear atomic at one level of abstraction

11


T-SON in action: multi-layered provenance
• Provenance of computed data naturally comes in layers:
– program execution (incl. workflow controller)
• system-level primitives, network protocols

10 r 10

t t 10 r 10
t
X

10 fetch send 10

X
f

Program
execution
get compute

t t t

f

Program
execution

Temporal abstraction used to hide/reveal lower-level details of both
12 systems and their interaction (i.e., reading from storage)

T-SON: multi-layered provenance
Additional unfolding:
- assume f is a service call
- reveal details of communication with an underlying service implementation

10 r 10

X

f

Program
execution

Service
execution

13


T-SON: multi-layered provenance

10 r 10

t t
t

msg msg
receive send
10 fetch send 10

Service
X
execution

msg msg
get receive
prep send

t t
t

f

Program
execution

14


Agents as evolving systems
Alice and Bob collaborate on document editing

An agent performs activities that account for changes in the state of the data
• F is data (a file)
• Data and agents are modelled as systems
• Each system is a SON
• Communication abstraction used to synchronize events across different

systems
• Bob.draft → F.write, F.read → Alice.”read draft” etc.
• For example, Bob in the state b2 is unaware of Alice’s feedback
• Bob in state b3 has read Alice’s feedback
15


Agents as evolving systems
• Tracking the state of agents is important
– we know that it is the “version” of Bob that is aware of Alice’s comment that is
responsible for the latest edit

Below: Bob’s edits to the document do not take account of Alice’s comments

ptd draft b2 edit b4

Bob

w f1 r f1 w f2 r f2 w f3

F

read leave
a1 a2
draft comments

16 Alice


Summary
• SONs extend well-known Occurrence Nets

• Simple graphical notation with formal grounding
– amenable to various types of analysis

• Appealing for capturing system evolution and inter-system
communication

• Accommodates multiple levels of abstraction

• Evolution traces of Data, Agents and Activities provenance queried
seamlessly

• Some software tool support (in progress), more work needed here

• Feedback for customizations of the SON model itself!

17


Selected References
•  V. Khomenko, M. Koutny, A. Yakovlev: Logic Synthesis for Asynchronous
Circuits Based on Petri Net Unfoldings and Incremental SAT. Fundamenta
Informaticae 70, 2006.
•  http://www.cs.ncl.ac.uk/publications/inproceedings/papers/749.pdf
•  M. Koutny, B. Randell: Structured Occurrence Nets: A Formalism for
Aiding System Failure Prevention and Analysis Techniques. Fundamenta
Informaticae 97, 2009.
•  http://www.cs.ncl.ac.uk/publications/trs/papers/1162.pdf
•  B. Li, M. Koutny: Verification and Simulation Tool for Communication Structured
Occurrence Nets. CS-TR, Newcastle University, (to appear).
•  P.M. Merlin and B. Randell: State Restoration in Distributed Systems. Proc.
FTCS-8, 1978.
•  http://www.cs.ncl.ac.uk/publications/inproceedings/papers/347.pdf
•  I. Poliakov, V. Khomenko, A. Yakovlev: Workcraft - A Framework for
Interpreted Graph Models. LNCS 5606, 2009.
•  B. Randell, M. Koutny: Failures: Their Definition, Modelling and Analysis. LNCS
4711, 2007.

•  B. Randell, M. Koutny: Structured Occurrence Nets: Incomplete,
Contradictory and Uncertain Failure Evidence. CS-TR 1170, Newcastle
University, 2009.

18 Martinique, Jan. 2012
24


IPAW 2012 - P.Missier EXTRA material

19


SON provenance and PROV

read
b2 b3 edit b4
feedback

Bob (a)

f2 r f2 r f2 w f3

F

used wasGeneratedBy
f2 edit wa f3 (b)
sG
en
era
used wasAssociatedWith ted
By
read wasGeneratedBy
feedback Bob_b3 wasDerivedFrom Bob_b4

wasAssociatedWith
wasDerivedFrom

Bob_b2
20


T-SON and finite-duration activities

In Occurrence Nets, events (activities) are instantaneous.
Using temporal abstraction one can add a time duration to activities

[s,e]
Activity f f
with duration [s,e]

t t t t t t

s e

c duration interval of f c

t1 t2 tn

Time

21


SON -- behavioural abstraction
• Insight: ‘system’ and ‘state’ are not separate concepts
• The same graph node may be used to represent either a state or a
system, at different levels of abstraction

Key idea of Structured Occurrence Nets:
• multiple ONs, each portraying a system/state at some level of abstraction

• associations amongst the ONs are then established by means of new
relation types

22


B-abstraction in use
– An application of behavioural abstraction -- state/system duality
– Bob’s state b1 expands into a system’s activities (b1)
– the expansion provides additional insight into Bob’s “knowledge level” /
“preparedness” prior to drafting the document

23 Bob’s state as a system

Finding good abstractions - cuts in ON and SON

(a)

(d)

(b)

(e)

(c)

24


Structured Occurrence Network for provenance: talk for ipaw12 paper

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Structured Occurrence Network for provenance: talk for ipaw12 paper