Grid-Based Decision Support with Pro-Active Mobile Computing

M. Ong, M. Alkarouri, X. Ren, G. Allan, V. Kadirkamanathan,

H.A. Thompson and P.J. Fleming

Rolls-Royce Supported University Technology Centre in Control and Systems Engineering,

Department of Automatic Control and Systems Engineering,

The University of Sheffield, UK.

{M.Ong, M.Alkarouri, X.Ren, G.Allan, Visakan, H.Thompson, P.Fleming}@sheffield.ac.uk

Abstract With the emergence of Grid computing and

service-oriented architectures, computing is

becoming increasingly less confined to traditional

computing platforms. Grid computing promises the

accessibility of vast computing and data resources

across geographically dispersed areas. This

capability is significantly enhanced by establishing support for mobile wireless devices to deliver access

to high-performance computing under demanding

circumstances. Access to the Grid from mobile

devices can be very effective in business

environments where users can access the vast computing power and data repositories on the Grid

while working out on the field. This also enables and

encourages collaborative working environments. A

Grid demonstrator system for distributed aircraft

health monitoring already developed and

implemented in the UK E-Science Grid project, DAME, is introduced. In this demonstrator, CBR

technology for decision support is implemented in a

practical framework that enables Grid-based, pro-

active mobile computing.

1. Introduction

With the recent advances in Grid computing and

service-oriented architectures, computing is

becoming increasingly less confined to the traditional

computing platforms of desktops, servers or

mainframes. While Grid computing itself promises

the accessibility of vast computing and data resources

across geographically dispersed areas, there is

currently a lack of established support for Grid-based

mobile computing. Grid-enabled computing with

mobile devices can be very effective in a multitude of

business environments. Users can have access to the

computing power and data repositories on the Grid

while working out on the field. Mobile Grid access

also enables and encourages distributed,

collaborative problem-solving environments.

A Grid-enabled mobile computing demonstrator

has been developed in the context of the Distributed

Aircraft Maintenance Environment (DAME) project.

The context for the demonstrator developed in

DAME is an aero-engine diagnosis and prognosis

problem (figure 1). This paper focuses on one of the

many DAME system components, the CBR

Maintenance Advisor, as an example of how Grid-

enabled services can be extended to handheld devices

for pro-active mobile computing (figure 2) to support

aircraft fault diagnosis. The developments reported in

this paper complements the developments in

optimisation [13].

Figure 1. Distribution of data in a virtual aircraft maintenance environment

2. Grid Computing

The Grid computing concept, first developed in

the scientific community, was initially aimed to

address the problems of sharing and working with

large datasets. Grid computing is now moving

towards a mainstream challenge of creating reliable,

robust, scaleable and secure distributed systems. The

Grid [2, 3] is an aggregation of geographically

dispersed computing, storage and network resources,

co-ordinated to deliver improved performance,

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

higher quality of service, better utilisation and easier

access to data. In this project, Grid computing has

enabled collaboration between numerous members of

the “virtual organisation” involved in the aero engine

maintenance scenario. This has enabled the sharing

of applications and data in an open, heterogeneous

environment. Compute-intensive decision support

tools previously considered to be host-centric can

now be distributed throughout a network of powerful

Grid nodes, improving quality of service while also

offering enhanced and improved capabilities. The

emergence of Grid software such as the Globus

Toolkit [4] provides the necessary middleware to

implement a Grid system and includes services that

tackle issues such as accessibility, security and

resource management.

The DAME project was implemented on a key

metropolitan Grid infrastructure, the White Rose

Grid [16], constructed between the partner

institutions Sheffield, Leeds and York at a cost of

£2.8M.

Figure 2. Service structure that enables access to a Grid-enabled service via the Internet on mobile handheld devices and conventional computers

3. Distributed Aircraft Maintenance

Environment (DAME)

Aero-engines are extremely reliable machines and

operational failures are rare. However, currently

great effort is being put into reducing the number of

in-flight engine shutdowns, aborted take-offs and

flight delays through the use of advanced engine

health monitoring technology. This represents a

benefit to society through reduced delays, reduced

anxiety and reduced cost of ownership of aircraft.

This is reflected in a change of emphasis within aero

engine companies where, instead of selling engines

to customers, there is a fundamental shift to adoption

of power-by-the-hour contracts. In these contracts,

airlines make fixed regular payments based on the

hours flown and the engine manufacturer retains

responsibility for maintaining the engine. To support

this new approach, improvements in in-flight

monitoring of engines are being introduced with the

collection of much more detailed data on the

operation of the engine. Advances made in Internet

technologies can provide a worldwide network of

computers that can be used to access and process that

data. The explosion of information within those large

datasets and a variety of diagnostic tools available

also presents it’s own problems. Here, it is necessary

to work on delivering advanced decision support

systems to the aircraft experts in order to aid

identification of useful information in the data and

provide effective diagnostic support between

individual aircraft, airline repair and overhaul bases,

world-wide data warehouses and the engine

manufacturer (figure 1).

The DAME project is a Grid pilot project

supported under the United Kingdom e-Science

research programme in Grid technologies [1,8].

DAME is particularly focused on the notion of proof

of concept, using the Globus toolkit and other

emerging Grid technologies to develop a

demonstration system. This is known as the DAME

Diagnostic/Prognostic Workbench. The demonstrator

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

system tackles complex issues such as security and

management of distributed and non-homogenous data

repositories within a diagnostic analysis framework

with distributed users and computing resources.

3.1. Diagnostic Scenario

A typical diagnostic scenario is as follows: The

on-wing diagnostic system and its associated ground

based system are used prior to the use of DAME. In

addition to that initial on-wing diagnosis, DAME is

always used to provide an automated diagnosis. This

is desirable because DAME can detect additional

situations, for example:

A recurring errant diagnosis

A new condition that has not been yet been

uploaded to the on-wing monitoring system

A condition that can only be detected using tools

that require extensive ground-based processing

facilities

The resultant automatic diagnoses can then be

assessed. In the vast majority of cases normal

situations are indicated, however, if a condition is

detected with a known cause then appropriate

maintenance action can be planned. Additionally, in

the rare case that a condition is detected without a

clear cause then the situation will be “escalated” to

one of various remote experts who can look into the

matter further. The Maintenance Analysts and

Domain Experts have access to the data from the

current engine flight, can run searches on historical

data, get workflow advice, run signal processing and

simulation tasks to gain an insight into any given

event.

3.2. Decision Support in DAME

It is clear that in order to deal with the explosion

in data available from complex engine health

monitoring systems, it is necessary to design

advanced decision support systems. These need to be

able to identify faults based on knowledge of

previous fault conditions and also perform analysis

across fleets of engines. A variety of on-wing control

system diagnostic techniques and portable

maintenance aid tools have been explored. The

research at the Rolls-Royce supported University

Technology Centre (UTC) at the University of

Sheffield has been based on two fundamental

underpinning technologies, Case-Based Reasoning

and model-based fault detection and isolation [12],

the first of which will be described in more detail.

3.3. Case-Based Reasoning

Case-Based Reasoning (CBR) is a knowledge-

based, problem-solving paradigm (figure 3) that

resolves new problems by adapting the solutions used

to solve problems of a similar nature in the past

[9,10]. A further advantage of this approach is that it

allows consolidation of rule knowledge and provides

a reasoning engine that is capable of probabilistic-

based matching. With CBR technology, development

can take place in an incremental fashion facilitating

rapid prototyping of an initial system. The

development of robust strategies for integration of

multiple health information sources is achieved using

reasoning algorithms of progressively increasing

complexity. In contrast to conventional search

engines, CBR systems contain a knowledge model of

the application domain in which it operates on. It is

therefore not universal but specifically designed for

the domain. Hence, it is possible to develop

intelligent search abilities, which even show

reasonable results when given fuzzy or incomplete

requests. Moreover, the results are ranked and

complemented by variants and alternatives, thus, not

only matches are given but information is valued

with "more suitable" or "less suitable".

Figure 3. CBR problem solving paradigm that builds upon previous knowledge

The work presented here builds on previous

research work which included investigating the use

of CBR techniques for a portable PC-based Flightline

Maintenance Advisor [6,7] to correlate and integrate

fault indicators from the engine monitoring systems,

Built-In Test Equipment (BITE) reports, maintenance

data and dialog with maintenance personnel to allow

troubleshooting of faults (figure 4). The outcomes of

the initiative included the implementation of a

portable Flightline Maintenance Advisor that was

trialed with Singapore Airlines.

Figure 4. Structure of the Flightline Maintenance Advisor

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

Today, rather than using a portable, stand-alone

computer that needs updating with new data as it

becomes available, it is highly desirable for a fault

diagnosis system to be accessed remotely by

engineers over a computer network. The advantage

of this is that it is easier to support and also allows

search of an extensive casebase of historical

maintenance incidents across an entire fleet of

engines [11] at a global scale. This allows

identification of the most appropriate course of action

to diagnose and rectify an engine problem with a

prescribed set of fault symptoms.

Essential to the CBR system is the casebase that

represents a knowledge repository containing

detailed descriptions of engine faults and the best

practice maintenance advice (solutions) gathered

from engineers and experienced mechanics over the

development and service life of the engine. For a new

engine type, little information is known initially but

the advantage of CBR techniques is that a casebase

of independent records of fault and maintenance

information can be developed in a piecemeal manner

and updated as and when knowledge about the

behaviour of the system is known. More importantly,

the siting of the CBR system within a virtual

maintenance facility also allows the integration of

diagnostic knowledge from multiple health

information sources which are vital in improving the

accuracy and coverage of the CBR knowledge

repository. Useful diagnostic information previously

available from separate monitoring systems, when

brought together into a single system, provides for a

more powerful diagnostic tool.

3.4. Service-based CBR

In support of the demonstrator, an in-house,

reconfigurable service-based CBR application has

been designed and implemented at the Sheffield UTC

as a Grid service. Grid services [5] are essentially

Web services with improved characteristics such as

state and life-cycle management. The CBR service

has been deployed in the DAME Grid computing

environment. Using a Web browser, aircraft

maintenance personnel can access this service via a

secure portal to the service from any computer

connected to the Internet. Fault information can be

submitted to the service directly via the Web browser

window (figure 5) or submitted automatically via an

integrated client such as the one in the DAME

automatic workflow system. The service processes

the fault information on a remote Grid node by

searching and matching across a large history of

cases and returns a set of ranked, closest matching

case.

The service can provide aircraft maintenance

personnel at various levels with access to stores of

accumulated diagnostic knowledge and maintenance

data. It is understood that with CBR, solutions

proposed for an unknown problem may not always

represent the ultimate solution but here it is important

to note that proposed solutions serve as a crucial

starting point for further analysis. At this point, the

user can select another diagnostic tool on the portal

that can utilise readily available Grid resources to aid

the decision-making process.

Figure 5. Web browser window displaying a result list of cases that match a query for a particular engine fault. For each brief case listed, the detailed fault information and maintenance advice can be obtained by retrieving the full case details

4. Mobile Handheld Device for Grid-

based Computing

In addition to the typical diagnostic scenario

described previously, a situation may arise where a

Domain Expert requires an analysis of a currently

occuring problem under demanding circumstances;

i.e. a conventional computer is not available to access

the DAME system. Furthermore, the ability of a

handheld computer to capture information on-site in

various forms and to instantly upload investigative

findings to the system on the Grid greatly increases

the accuracy of CBR in diagnosing the problem. The

rapid sharing of real-time information across the

DAME environment enables several engine experts

at distributed locations to collaboratively solve the

problem, thus reducing aircraft down-time and costs.

A mobile computing device such as the widely

available Personal Digital Assistant (PDA) presents

various problems such as hardware constraints, small

graphical display area and security issues. The

limited local processing power and built-in memory

available means that applications need to be

efficiently implemented and this may mean

excluding the use of complex programming

environments/frameworks. Software development for

mobile handheld devices tend to be more complex to

take into account the device’s operating system and

hardware platforms. A small display area usually

found on such devices can also make presentation of

information to the users a challenging task.

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

4.1. PDA Demonstrator System

In order to overcome these limitations, a

demonstrator consisting of a PDA that utilises the

previously mentioned Grid-based CBR service was

developed for aero-engine fault diagnosis. The device

itself is a widely available HP iPAQ device that

features a built-in wireless network interface and

Web browser. Using a standard Wi-Fi (802.11b),

Bluetooth or GPRS (over GSM) wireless Internet

connection, the PDA is able to access services

available on the Grid, thus offering the benefits of

distributed, high performance computers required to

achieve the desired tasks (figure 2).

The current capabilities of PDAs make it

impossible to have a complete Globus toolkit

equivalent implementation on the device. This

mandates the use of a proxy that will interact with the

Grid environment while providing suitable access for

the device, and a client for this proxy on the device.

Here, a mini Web portal is used as a proxy, enabling

the device to access the Grid using a standard, built-

in mini Web browser as a client.

The mini Web browser represents the front-end to

the system on the PDA that allows the user to access

the customised Web portal to the Grid service. This

portal is very similar to the standard portal accessed

by conventional desktop computers, the difference

being that the mini-portal is simplified by the

removal of complex script functions normally aimed

to enhance the layout of content on larger displays.

Furthermore, the page layouts are rearranged such

that every page executes a single operation at a time,

both for display purposes and to optimise on

bandwidth usage. The mini portal can deliver a

similar quality of results to the user whilst

minimising the graphical content load on the PDA

display.

When in use, the PDA can search and match a

currently occuring problem, given initial information

about the problem, with a large archive of historical

cases on the Grid. Matching cases (figure 6) can be

adapted to form a new case to represent the current

problem. Additional knowledge gained from further

analysis, such as vibration information (figure 8),

digital photos or even audio/video media can be

appended to the case in real-time as it is being

investigated, making it available across the Grid and

if necessary escalated to an expert at a different

location. It is this model of collaborative problem-

solving that is defined in this paper as pro-active

handling of the currently occuring situation by the

right person, in the right place at the right time.

The identification and successful solution to the

problem can finally be appended to the case via the

same interface and stored on the Grid as “new

knowledge” for future use (figure 7). To support the

diagnostic process, compute-intensive engine

performance simulations, normally a time-consuming

task, can be executed on the Grid and the results

retrieved on the PDA. Figure 9 shows an abnormal

spike identified in the engine data relating to the

occuring problem that was made available to the

engineer via the PDA.

Figure 6. PDA’s Web browser window displaying the result list from a search for cases that match a currently occuring problem

Figure 7. In-depth details and maintenance advice can be retrieved, viewed and appended on the PDA

The software and standards used for this

particular demonstrator system is based on widely

accepted Internet standards thus it is highly feasible

for the system to be implemented across various

other applications areas. The increasing availability

of wireless networks and advances in Grid

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

technology provide a strong case for wireless, Grid-

enabled decision support with mobile computing

devices.

Figure 8. Time series vibration spectrum data for problem in question is available on the PDA for further investigation.

Figure 9. Spike in engine data from the model simulation indicates the cause of the fault to the diagnostic engineer using the PDA

The capability displayed by the demonstrator

system is particularly important because it offers

aircraft experts, considered as a high-value resource,

the mobility to pro-actively operate on large data and

complex problems under demanding circumstances.

Similar scenarios can occur in many diverse IT

domains such as healthcare, engineering, finance and

environmental sciences. However, regardless of the

application area, the systems share a number of

similar operating and design characteristics, making

it possible to experience similar benefits of Grid-

enabled, pro-active mobile computing. The next

section describes how emerging service-oriented

technologies have been used to support the

framework that enables that.

4.2. Service-Oriented Architecture

Service-oriented architectures (SOA) are

essentially a collection of services, focusing on

interoperability and location transparency. These

services communicate with each other, and can be

seen as unique tools performing different parts of a

complex task. Communication can involve either

simple data passing or it could involve two or more

services co-ordinating some activity. SOAs and

services are about designing and building system

using heterogenous network addressable software

components. An important aspect of the SOA is that

it separates the service’s implementation from its

interface. Web services, are services offered via the

Web.

In the demonstrator scenario, the browser

application initiates a request to the CBR service at a

given Internet address using the SOAP1 protocol over

HTTP2. The CBR service receives the request,

processes it, and returns a response. Based on the

emerging standards such as XML3, SOAP, UDDI

4,

and WSDL5, the CBR service along with other

services in the DAME system form a distributed

environment in which applications, or application

components, can inter-operate seamlessly across the

virtual organisations in a platform-neutral, language-

neutral fashion. The CBR service consumers can

view the service simply as an endpoint that supports

a particular request format or contract. Consumers

need not be concerned with how the CBR service

goes about executing their requests; they expect only

that it will.

Grid computing support for the CBR service is

provided by means of implementing Open Grid

Services Architecture (OGSA) concepts with web

service technologies. The CBR service benefits from

both web service technologies as well as Grid

functionality. Compute-intensive tasks within the

1 SOAP - Simple Object Access Protocol 2 HTTP - Hyper Text Transfer Protocol3 XML - eXtensible Markup Language 4 UDDI - Universal Description, Discovery and Integration 5 WSDL - Web Services Description Language

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

CBR matching process, previously computed locally,

are now aggregated across the available compute

nodes using Grid middleware, the Grid’s effective

operating system [4]. With this, multiple instances of

the service are created on-demand to allow multiple

consumer requests to be processed simultaneously by

separate nodes of the Grid (figure 10). With the CBR

service as a prime example, the integration of Grid

computing with Web services can provide aircraft

experts at any remote geographical location with

access to powerful diagnostic tools, data repositories

and large computing resources to support that via a

mobile handheld device.

Figure 10. Multiple instances of the CBR service are distributed for processing on Grid nodes, each instance supporting an individual process

4.3. Security

A Grid-enabled decision support system may

contain potentially business-sensitive data and hence

access to data and services should be restricted to

authorised members within the virtual organisation.

For instance, both the CBR knowledge base and

engine models could contain important information

on aero-engine design characteristics and operating

parameters. The use of the Grid Security

Infrastructure (GSI) [14] enables a system for secure

authentication and communication over an open

network. GSI consists of a number of security

services including mutual authentication and single

sign-on. This is based on public key encryption,

X.509 certificates, and Secure Sockets Layer (SSL)

transmission. The implementation of GSI within the

DAME decision support environment is composed of

Globus Toolkit 3 (GT3) security elements

conforming to the Generic Security Service API

(GSS-API), which is a standard API for security

systems promoted by the Internet Engineering Task

Force (IETF).

At the core of the GT3 security infrastructure is

client and host authorisation using X.509 identity

certificates for both the service users and service

hosts. Hence, all users and service hosts need to

acquire a certificate issued by a trusted Certificate

Authority (CA). Because the CA is the heart of the

security system, it is very important that Grid hosts

and users only use their own trusted CA or an

established commercial CA. A CA’s signing policy is

placed in the Grid computing environment to allow

nodes to authenticate users holding valid certificates.

On top of this, users have their user credentials listed

on a Grid-Mapfile. The Grid-Mapfile is a file used to

store mappings between a user identity on the Grid to

a local identity (an account name on the Grid

computer being used). DAME system users are only

allowed to access the decision support services and

Grid resources on any Grid node if their verified

credentials have been registered beforehand by the

Grid administrators.

5. Concluding Remarks

This paper described how Case-Based Reasoning,

one of the core technologies available for health

monitoring in DAME has been developed to extend

the benefits of Grid computing to mobile handheld

devices. Although developed for the aero-engine

problem, the pro-active PDA implementation along

with its service-based architecture is applicable to a

variety of domains involving distributed data sources

and dynamic working environments. The PDA

demonstrator has shown that Grid-enabled computing

from mobile devices can be very effective in a

Proceedings of the 2005 IEEE International Conference on Services Computing (SCC’05) 0-7695-2408-7/05 $20.00 © 2005 IEEE

business environment by providing access to

powerful services and Grid functionality under

demanding circumstances. This also enables and

encourages distributed, collaborative working

environments. In the future, the demonstrator

framework presented in this paper is also highly

applicable within crisis management scenarios where

teams of mobile workers, such as paramedics, police,

firefighters or military personnel need to collaborate

in critical situations. Access to real-time information

and knowledge, simulation of the situation,

optimisation and logistics support can greatly

improve the decision-making processes for pro-active

management of the situation.

Acknowledgements

The authors gratefully acknowledge financial support

of the Engineering and Physical Research Council in

the UK under Grant Number GR/R67668/01 and

contributions from Rolls-Royce plc and Data

Systems & Solutions, LLC.

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