Web Services Extension Model Simulation In

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at the client-server sides and the communication agents [6]. .... These CPNs are called pages (or subpages) and are related ..... dot, in dot's User's Manual. 2006.
2012

International Conference on Computer & Information Science (ICCIS)

Web Services Extension Model Simulation In Hierarchical Colored Petri Net Dani Adhipta, Mohd Fadzil Hassan, Ahmad Kamil Mahmood Computer and Information Sciences Department, Universiti Teknologi PETRONAS Bandar Seri Iskandar, 31750 Perak, Malaysia

Abstract-This paper presents the modeling in Web Services (WS)

extension

performance

by

(WS-E)

for

higher

Representational

Net

(HCPN)

model

is

fairly opaque due to its message encapsulation during the

Transfer

(REST)

endpoints traversal which reduces the property of loosely­

State

Hierarchical Colored Petri

constructed

for

However, SOAP is well-known to be

transfer

architecture style and Abstract Syntax Notation One XML Encoding Rule (XER) adoption.

environment [3].

message

the

WS extension

coupling among its peers communication [4]. HTTP

allows

a

certain

degree

of

SOAP over

intermediary

for

framework formalization. The validation and verification of

communication agent but decoupling the peers may require

the model is performed by analyzing the generated State Space

extra efforts due to partial message in-transit transparency.

(SS).

Furthermore, the general defacto message format based

It is the aim of this paper as a proof of concept of the larger

research titled "Web Services Extension Model in Colored Petri Net to Enhanced the Message Transfer Performance", an architectural

extension

proposal

to

the

current

remote

laboratory remote instrument connected to the grid for facility sharing aimed at higher communication performance.

on eXtensible Markup Language (XML) is highly verbose and relatively larger in size since the content must be intelligible to human hence inefficient for machine-to­ machine transport

For message size reduction to

[5].

achieve higher rate of communication,

XML must be

encoded using common standard algorithm understood both I.

at the client-server sides and the communication agents [6].

INTRODUCTION

The need for higher performance data transfer for the

Grid's remote lab toward sharing instrument/sensor within a virtual organization has initiated the motivation of this research area.

The primary objective is web services

extension (WS-E) model in hierarchical Colored Petri Net (HCPN) to the current framework by incorporating Abstract

Syntax Notation One's XML Encoding Rule (ASN.I XER)

Arising from this need, a WS extension (WS-E) to provide alternative solution is proposed.

The extended

framework is studied, formalized, designed, modeled, and analyzed as proof of concept.

The model in HCPN is

verified by analyzing its State Space properties to evaluate

the 'correctness' when simulated using real-world data to validate its performance improvement.

for message size reduction and adopting Representational

III.

State Transfer (REST) architecture style to improve the

RELATED LITERATURE

As part of the current Grid middleware, Globus Tele

loose coupling and scalability properties while supporting transparent intermediary of the service oriented architecture

Control Protocol (GTCP), Common Instrument Middleware

in wide area network. The model simulation replications are

Architecture

performed to obtain the results. State Space of the WS-E

Instrumentation with Distributed Control and Computation

(CIMA)

and

Grid

Enabled

Remote

model is validated and verified for its correctness in terms of

(GridCC), are the choices yet competing efforts in providing

Petri Net token marking's

Grid to remote instrument integration in heterogeneous

discover

the

structural

transitions properties.

liveness and reachability to

interconnection

of

places

and

The aim is to provide the higher

message transfer performance toward heterogeneous data sources

while

promoting

further

interoperability

Coined by [9] REST has gained momentum since then, it

achieve efficient and economical in performing massive computation and conducting virtual remote experimentation between distant sites [I]. The scientific community has the need for higher performance of message transfer from the current of 1�2 cycle per second up to 7�8 folds to perform their experiment using remote lab instrument within the Grid virtual organization adequately [2]. The Grid middleware, such as Globus Toolkit (GT) and gLite, employ common WS framework based on Simple Protocol

Architecture (SOA)

(SOAP)

in

an

architectural

style

(not

a

standard)

to

establish

foundation how the web should be and work. Hypermedia

BACKGROUND

Sharing resources is the essential purpose of the Grid to

Access

attempting to provide standards [8]. is

II.

These instrument middleware (1M) are

based on WS framework for the interoperability while

and

scalability.

Object

environment [7].

Service

Oriented

for interoperability in client-server

utilization,

loose-coupling,

intermediary,

and

uniform

interface are the fundamental desired properties for the web based services [10]. when

fully

According to this architecture style,

supported,

the

web

will

be

interoperable,

scalable, simpler yet fully functional as what the web should be. REST hypermedia engine implies that the resources as services will have unique uniform resources identifications (URis) and the access are performed via links navigation. In other words, RESTful style dictates that web services must expose its resources identified by URI [11]. ASN.I

has

been

around

and

utilized

in

the

telecommunication industry for over than 20 years [12]. It

978-1-4673-1938-6/12/$3\.00 ©2012 IEEE

[741 ]

2012

International Conference on Computer & Information Science (ICCIS)

is a well-proven technology (and algorithm contained) to

simpler term. The random variate value generators provided

produce efficient data transfer at lower layer (hardware

by the CPN tools are:

level). In the last few years ASN.l has gained popularity in the

emerging

internetwork

for

web

services



data

uniform(a:real, b:real) : real exponential(r:real) : real

communication. The effort of incorporating ASN.l into web



normal(n:real, v:real) : real

services, such as Fast Web Services (FWS), to produce



erlang (n:int, r:real) : real

smaller message size while retaining the SOAP has been established [13]. However since SOAP over HTTP does not fully conform and comply with RESTful style, the inherited outstanding issues mentioned previously are still present [14].

In this research, although consideration to utilize the

highest message size reduction such as Packed Encoding Rule (PER) has been investigated, ASN.l

XER is the

middle-ground solution that is still intelligible to human for analysis/debugging

and

easily

processed

format

while

giving the size reduction needed for the Grid's remote instrument message transfer, is the most logical encoding rule to employ [15]. A modeling is the primary approach to realizing the proposed

WS-E.

Henceforth,

bipartite

graph-theory

mathematics based Petri Net is utilized to explain and formulate flow process [16].

Colored Petri Net adds time

property to the 'colored' or attribute of each token's (it is also called marking) [17, 18]. IV.

Henceforth, WS-E model utilizes few of these libraries to provide the set stochastic functions to simulate the real­ world behavior. The model is constructed from the initial state then all reachable State Space must be calculated.

In order to

properly simulate, the constraint mentioned above must be fulfilled.

The WS-E CPN becomes a reachability graph

with timed values as the colored to the token's marking. All results produced as the outcome of State Space calculations. The Strongly Connected Components (SCC) is the support that each

state

is alive

and reachable while allowing

conditional branching to determine the course of the token traverse according to the marking.

In WS-E HCPN, dead

marking indicated in the State Space report, demonstrate the nondeterministic behavior of the model, i.e. packet loss is allowed and message retransmission from the server is reattempt.

The

State

Space

analysis

of

model-based

verification of finite-state concurrent system involves set of reachable

HIERARCHICAL COLORED PETRI NET

Colored Petri Nets (CPN) is convenient for specifying complex concurrent systems.

markings

(nodes),

occurrences

of

binding

elements (arcs), and occurrence sequences (paths).

The property of CPN has

The

realization in the CPN tool itself is simply the collection of places and transitions connected by arcs.

CPN Tools also

mainly been specified directly in terms of the State Spaces

provides

(SS).

generated State Space graph to find the dead markings (valid

The temporal logics, such as CTL, is useful for

expressing properties of concurrent systems [19].

Primary

utilization of CPN is for analyzing a typically model-driven to allow what-if questions in the form of reachability graph. Typical

CPN

model

types

are

aimed

at

validation,

verification and performance analysis. Petri Net is based on graph theory by possessing the moving token (marking) from places through transitions. events

(transitions)

by

having

a

well-defined

formal

semantics for true concurrency instead of interleaving.

appropriate

functions

for

querying

the

termination states or deadlocks) in order to check the

model's safety and liveness properties. In order to satisfy the statistical minimum requirement to obtain simulation results

[21],

subruns and confidence

intervals must have •

replication of multiple runs since a single run does not



mutually

In other words, CPN

provides an explicit representation of states (markings) and

the

provide information about reliability of results independent

runs

to

further

calculate

a

confidence interval, e.g., the flow time is with 95% confidence within the interval 5.5+/-0.5 [5,6].

Simulation is the most commonly used analysis technique and from CPN technical point of view, it is the traverse of

its tokens throughout the reachability graph.

The tokens'

transient behavior, according to the given set of marking (or colors),

enables

indicators.

the

timed

properties

for

performance

It is, however, only an approach method when

the real-world representation is not available. CPN utilizes State Space in its analysis technique; hence, the constraints below must be fulfilled: •

Events or occurrences must finite in sequences, or break-point (or stop-signal) can be employed



Reachability enables transition in occurrence sequence



Bounded limit must hold upper value for all reachable

to identify deadlock markings The basic of CPN is the stochastic process in which the simulation of nondeterministic system made possible. timed

nondeterministic

probabilities described by

system,

the

In a

durations

and

the given distributions

[20].

Therefore, CPN is to simulate a stochastic process, in

[742 ]

V. WS-E HCPN CONSTRUCTION The WS-E model is designed mainly emphasizing on message

synchrocity,

partial

cacheability,

out-of-order

(nonsequential) message transfer, and data reconstruction at the receiving end.

Concurrency for multiple senders, are

constructed however this research only focuses on dual servers and clients, or receiver, to simplify the initial model. Nondeterministic characteristics due to real-world nature of message transfer is controlled by message guard to ensure the correct sequence order during data reassembly, i.e., message may be delayed, discarded if unsafe, or rearrange when necessary. assigned

to

CPN token color, or time attribute, is

simulate

the

real-life

typical

network

performance. The Hierarchical Colored Petri Net (HCPN) includes additional features such as substitution transitions and fusion places [22].

The underlying idea in HCPN is to use a

number of small CPN in order to develop a complete model. These CPNs are called pages (or subpages) and are related

2012

International Conference on Computer & Information Science (ICCIS)

to each other in a well-defined way.

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