Molde University College INF 245 Fall 2007 OBø 1 INF245 Application Architectures H 2007 Ola Bø

Molde University College INF 245 Fall 2007 OBø

1

INF245Application

Architectures

H 2007

Ola Bø


2

Architectures

Four main architectures Wireless internet aka thin clients Smart clients Message based Ultra thin architecture – terminal clients

Architecture is important How to choose the right architecture? What are strong and weak properties for each

architecture? The purpose of this lecture is to answer the two

questions above.


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Factors that determine the choice of architecture Target users: who, technical skill, scenarios for use Mobile devices: Is there an installed base or can we select devices for

the job? – if so what is the most appropriate device Connectivity: How to connect. Is wireless necessary. What kind of

wireless. Data quantity vs. connection Data: Quantity. Where is the data, can it be downloaded at the spot or

do they have to exist in the device. How volatile is the data, local vs. central data?

Integration: How to access other systems. Are they available over the Internet?

Security: Is the information sensitive. How can the information be stored on and transferred to and from the device in a secure way. Is the local data store secure against break-ins. What about authentication, viruses. What if the device gets stolen?

Battery time. Is it a problem. What about consumption for wireless, charging during the workday, backup batteries?


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Application architectures

TerminalClient?


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Applications based on wireless web

Gateway

Uses different markup languagesWML cHTML XHTML

Some browsers can prestore internet pages. (web clipping)

Can deliver content in different markup languagesWML cHTML XHTML


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Architectures built upon wireless www advantages

Easy to install on the device an extension of existing

Internet applications User Interface is well

known – no extra training Simple integration with

other applications using Internet

Available on many mobile devices

Data always up-to-date Security

disadvantages Wireless access is

essential Bad performance due to

latency time and bandwidth limitations

Security Communications cost Still rudimentary browsers

No scripting? no ajax? weak CSS support?

Primitive user interface Considerable browser

heterogeneity Testing difficult

Discussion: Will disadvantages decrease in the near future?


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Applications built upon wireless Internet

Here are some applications best implemented using wireless internet Stock trading Information services

News, weather, sport M business


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Smart client architecture

Devices may store data locally

May work without a wireless connection

Updating is called synchron-isation

The smart client may be developed by using either the J2ME platform or by using the device operating system as a platform. Provisioning is a problem?

A synchronisation server is responsible for same information in the central and mobile databases.


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Advantages and disadvantages of smart clients

Advantages may work locally without

connection data is always available rich user interface better performance distributed computing security lower communication

costs better autonomy

Disadvantages More difficult integration More difficult provisioning More difficult

maintenance Complex development

for heterogeneous platforms

Security


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Applications for smart clients Smart clients should be

considered when Wireless connection is not

available or has too low bandwidth

We need a more advanced user interface for example for gaming

We must use resources not available from a thin client: GPS, Camera, RFID-reader

We can save data transfer time and cost

The application is free-standing

Samples Sales Force Automation –

essential to have data present when meeting customer

Field Force Automation- Support for service technicians Information and task

Health-service Data collection services

inventory surveys


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Message based architecture Many possible messaging technologies

User to user email, sms, im, mms

Can also be generated by servers Alerts and alarms

WAP push, sms Application to application

The device must have a smart client using messaging to communicate

Message Queue Properties of message-based architectures

Messages that can not be forwarded are stored Stored messages will be sent when possible Can be combined with other architectures


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Message based application to application architecture


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Advantages and disadvantages of message based applications

Advantages: Message handling is

preinstalled and most users are familiar with it.

Messages are pushed Can fill in missing two-

ways communication in pull based architectures

Store and forward robust when bad wireless

coverage Many technologies to

choose from

Disadvantages User has weak support

when entering messages (no form or labels) Syntax must be simple Only simple interaction

is possible Application to application

messaging may be complicated


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Message based applications

Popular in consumer-applications Communication Entertainment Information dissemination

Business applications Efficient for information exchange

Asynchronous Extension of existing apps Alarms if certain events


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Mobile applications may benefit by combining with desktop

Some use cases fit better to a desktop workstation Is a workstation available?

Some of the use may be done on a workstation Order airplane tickets Manage appointments Find the auction Get an overview of the

inventory Touch up images

Some use cases may be done on the mobile unit Is the plane delayed? Check address for next

appointment and find the way

Get information about the last bid and enter a new bid

Count inventory Take picture

The common pattern is using the desktop when you need an overview over large amounts of data using a good user interface. The mobile is used to handle smaller amounts of information in a mobile context. The same application may be used on both.


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How to exchange data between workstation and mobile device

Synchronization Data are updated on stationary and mobile

automatically according to rules File transfer

Data are transferred using object exchange via BT or IR

Both units are using the same server, site or database If a smart client has a local database, the

databases may be synchronized.


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Solutions based upon terminal client and terminal server A terminal client transmits

all input to server and displays visual output from the server

A terminal server runs many user sessions interpreting input and generating screen output

This can be done with surprisingly low bandwidth

Can be developed as an ordinary desktop app, but using limited IO

The terminal server has full connectivity

May continue session after communications break

But no communications => no application


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TC/TS Solutions pros and cons Advantages

Easy installation? Easy upgrades Don’t need to learn a new

environment No browser heterogeneity Powerful platform No need for software to

handle communications breakdown User reconnects to the

same session No extra database

complexity

Disadvantages Wireless access is

essential Terminal client must be

installed Screen size must be

standardized and not too small

No access to device resources?

Communications cost IO different from platform IO


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Exercise

The maintenance workers of a manufacturing company are servicing machines in production facilities in a number of sites within a large area. For each service job there is an there is an operating procedure and possibly drawings of the equipment to be serviced. The part inventory database and the log for service jobs should also be available and updatable. The service jobs are done regularly on a weekly to yearly schedule. The maintenance is done partly in places that are difficult to access demanding climbing ladders or passing through narrow openings. It is an advantage if the mobile equipment is available when the work is being carried out. The workers also need to communicate with each others and with the maintenance managers. Some of the work places ar without GSM or WLAN coverage.

Exercise: Suggest use cases, application architecture, and what wireless network and what kind of mobile devices may be sutable for an application supporting the activities described


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Exercise

You are working with an application to support ornithologists. The main goal of the application is to enable registration of birds in an area. The date being registered are species, number of adults, number of eggs/offspring, date, time and comment. The registered information shall be transferred to a central data base. In rare cases, the ornithologist is in doubt as to which species he is observing. Therefore images and sounds for all species should be available on the mobile device. Some of the areas being observed are outside the coverage area of mobile networks.

Exercise: Suggest use cases, application architecture, and what wireless network and what kind of mobile devices may be sutable for an application supporting the activities described


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Exercise

After testing opinion using a questionnaire there is a substantial amount of supplementary work punching the questionnaires into the database of results.

The cost and number of errors committed can be reduced by registering the answer directly into a database while the respondent is answering.

Your job is to plan a mobile application that is practical for the employees of the opinion surveying agency when the surveying is being done by walking from door to door in an area or by stopping people in the street.

Suggest use cases, application architecture, and what wireless network and what kind of mobile devices may be sutable for an application supporting the activities described


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Exercise

Petrine’s Pizza wants to make it possible for customers to order pizzas from mobile devices. The customer should receive response confirming that the order has been received and telling when the pizzas will be delivered.

Discuss the pros and cons of implementing this as an sms-service versus as a thin client solution.

Why are smart clients inappropriate for this application?

Documents

Molde University College INF 245 Fall 2007 OBø 1 INF245 Application Architectures H 2007 Ola Bø