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- Chapter 5
- Information Systems Management In Practice 5E
- McNurlin & Sprague
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- Degree to which a system is distributed can be determined by answering
four questions:
- Where is the processing done?
- How are the processors and other devices interconnected?
- Where is the information stored?
- What rules or standards are used?
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- Distributed processing is the ability for more than one interconnected
processor to be operating at the same time. Goal: move the appropriate processing
as close to the user as possible and to use computers that do part of
the job the best. Permits
interoperability-capability of different computers using different O.S.
on different networks to work together on tasks. Two forms of
interoperability (capability for different machines to work together on
tasks):
- communication between systems
- two-way flow between user applications
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- Connectivity among processors means that each processor in a distributed
system can send data and messages to any other processor through
electronic communication links.
Desirable to have at least
two independent paths between two nodes to provide automatic
alternate routing.
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- Distributed databases either divide a database and distribute its
portions throughout a system without duplicating the data or store the
same data at several different locations, with one site containing the
master file.
- Issue: synchronization of data
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- System wide rules mean that an operating discipline for the distributed
system has been developed and is enforced at all times. “Open systems” concept-mix products
from vendors using open std. Based on “open-systems” - standardized
interfaces that allow products to inter-operate across multi-vendor
networks, e.g., UNIX OS. Define
the communication between nodes, security, data accessibility, program
and file transfers, and common operating procedures. API’s - Application program
interfaces: define the way to present data to another system component
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- Are the operations interdependent?
- One operation knows what other is doing. If yes, their planning,
development, resources, and operations must be centralized.
- Are the businesses really homogenous?
- Have a lot in common; e.g., IT needs for a fast-food franchise,
processing distributed, planning and hardware selection centralized.
- Does the corporate culture support decentralization?
- A decentralized business hierarchy might still centralize finance, HR,
and systems planning.
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- Organizational - (see Figure 5-1):
- Locate processing power and dB at each level in the organization. Top
three levels are traditional domain of IS, where computers resided in
the past. Bottom three levels are where the bulk of employees are.
Intent: give autonomy and decision-making power to better serve
customers.
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- Technical - (see Figures 5-2 & 5-3):
Migration of computer power to end users will be driving force
for network-based IS. SUMURU - single user, multiple user, remote
utility.
- Processors:
- SU: single user, stand-alone and connected to LNs; clients
- MU: multiple user, serve local groups of users; server. Also heavy duty
computation for SU’s, backups for MU’s, program libraries for SU’s, and
dB management.
- RU: remote utility, heavy-duty computing, corporate dB management,
corporation mainframes and value-added network services
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- Networks:
- LN: local networks, high-speed information transfer, LAN
- RN: remote networks, lower transfer speeds, WAN, MAN, Internet
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- Services that this network architecture provides:
- access
- file transfer
- e-mail
- Standards needed in three areas:
- OS
- communication protocols: TCP/IP
- DBMS: SQL
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- Six distributed architectures:
- Host-Based Hierarchy (see Figure
5-4):
- A central, controlling mainframe at the top, PCs at the bottom,
minicomputers in between. Master/slave. First data processing
distributed system. Host computer central, controlling component;
terminals are access systems. Where is the data stored?: could be at any
level.
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- Decentralized Stand-Alone Systems
- (see Figure 5-5):
- Decentralized but does not form a distributed system, “islands of
computing,” little data flow amongst, except upward to corporate
systems.
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- Peer-to-Peer LAN-Based Systems
- (see Figure 5-6):
- No hierarchy, “peer-to-peer” communications, interconnecting LANs rather
than hierarchical communications through a central hub. No “superior”
computer.
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- Hybrid Enterprisewide Systems
- (see Figure 5-7):
- Combination hierarchy (mainframe-based, favored for corporate computing)
and LAN-based (favored by departments). The structure of choice for many
years. Allows company to link “automation islands” and retain IT
investments, begin to automate business processes (cooperative
processing).
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- Purpose: to audit all the redeemed tickets to calculate revenue
accurately.
- The system uses a cooperative processing architecture and integrates
expert systems, image processing, relational databases, high resolution
UNIX workstations, servers, and LANs.
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- Lessons learned:
- Benchmark and prototype new technologies to verify vendors’ claims.
- An open architecture works on mission-critical applications.
- Large distributed system projects need a vendor coordinator.
- Use of CASE was mandatory.
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- Client-Server Systems:
- The 90s version of distributed systems, splits the computing workload
between the client, which is a computer used by the user and can sit on
the desktop or be carried around, and the server, which answers the
request. Trend: three-tier
- architecture (see Figure 5-9).
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- Tier 3: the superserver/mainframe.
Allows to include legacy applications, short-lived and
fast-changing data, and integrity rules.
- Tier 2: specialized servers, dedicated to housing databases or
middleware-software to ease connection between client and server. Also, department-specific data that
does not change often.
- Tier 1: clients, connected through network.
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- Figure 5-8 shows the possibilities for splitting work between clients
and servers. Three components being split are:
- Presentation software: what user sees (P)
- Application software (A)
- Data (D)
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- Spectrum:
- Distributed: D, A, P at remote server. Leave mainframe legacy in place
w/ graphical output
- Remote presentation: P on client, D & A on server. Also preserve
legacy systems
- Distributed: P client, D server, A split C/S. Complex, coordination to
split application. Appropriate for A as packaged software (s/s,WP)
client as corporate application. Also mobile computing.
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- Spectrum: (cont.)
- Remote data mgt.: P & A on client, D on server. Popular, all A in
one place - fat client and takes advantage of large processing capacity
on desktop.
- Distributed database: P & A & some D on client, remaining D on
server. complex, important for
mobile computing, local and less dynamic data, fat client.
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- Benefits of Client-Server Computing:
- Better access to information: improved customer service, ability to
communicate customer needs, and anticipate customer needs. Reduce cycle
times and allow companies to compete better.
- Empowered employees: blend autonomy of PCs with system wide rules and
connectivity of traditional IS. Shifts focus of computing to users.
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- Benefits of Client-Server Computing (cont.):
- Increases organizational flexibility: allows new technology to be added
more easily without affecting rest of system; streamlines work flow
between functional areas; encourages people to work together via
networks.
- Drawbacks:
- not lower in cost than mainframes; entail much coordination
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- Internet-Centric Systems: “thin” client machines, run like telephones,
no hard-disk but browser, memory, kb, modem. For consumer applications
and hand-held devices.
- E.g., for extranet applications, such as global broker-dealer
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- To describe the IS architecture, look at the roles people and components
play:
- Rows: Views must be taken into account when building complex products:
planner (scope statement), owner (model of the enterprise), designer
(model of the information system), builder (technology model),
subcontractor (description of the components), and user (functioning
system).
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- Columns: IS components - data models (what it is made of), functional
models (how it works), and network models (where the components are
located); represent physical manifestations of the system. Also people (who), time (when), and
motivation (why).
- Use of the framework: When IS users bring in a package that follows a
data model inconsistent with the rules of the company, a lot will be
spent fixing the package.
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- Four types of investments (see Fig. 5-14):
- Strategic investments: aim to change the way a firm competes, intends to
increase revenues, longer term so income stream is difficult to estimate
- Informational investments: provide a firm with information employees
need to manage and control the organization, e.g., accounting, EIS, medium term
horizon, depend on lower two levels
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- Transactional investments: support operational management; intended to
cut operating costs by substituting capital for labor, handle larger
volume
- Infrastructure investments: provide foundation of IT capability in a
firm; supports applications
- IT infrastructure includes networks, DW, computing facilities, EDI,
applications sit on top
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- IT investments can provide:
- Economies of scale (utility): infrastructure cost as an administrative
expense, minimize expense
- Support for business programs (dependent): infrastructure treated as
business expense, measured by short-term business benefits,
infrastructure planning in current business plan
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- Flexibility to meet changes in the marketplace (enabling): primary
benefit long-term flexibility, intended to provide the foundation for
changing direction in the future, IT cost seen as business investment
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- Distributed systems dominate the computing environment
- They create an enterprise architecture to cope with complexity of
change.
- IT infrastructures should provide the platform for allowing
interconnection and organizational flexibility.
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Notes
