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PROGRAMS - PowerPoint PPT Presentation

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PROGRAMS. The categories of programs for workgroup information systems are system programs, including OS utilities, DBMS, & applications programs (same as personal information systems). Network OS. Each comp must have a local OS program - DOS & a network OS program.

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  • The categories of programs for workgroup information systems are
  • system programs, including OS utilities,
  • DBMS, &
  • applications programs
  • (same as personal information systems)
network os
Network OS
  • Each comp must have a local OS program - DOS & a network OS program.
  • The relationship between the Network OS
  • & other programs.
  • It also has a DBMS & database application
  • & also other application programs
  • The Network OS supports LAN processing & must match the processing style of the network cards in use.
network request processing
Network Request Processing
  • LAN has to have a Network OS that does the functions of level 3 to 6 of OSI.
  • Remember this:
  • Topology & cabling --> layer 1 of OSI
  • Now Data-link protocol --> layer 2 of OSI
network request processing1
Network Request Processing
  • Suppose user transfer file CH9.doc from local drive
  • C: to network server device F: & place it in dir TEXT:
  • (COPY C:\CH9.DOC F:\TEXT) (consider previous figure)
  • 1. Command sent to DOS
  • (w/in DOS there is a piece of netw OS, which cuts through the command)
  • 2. If command involves network device (this ex yes),
  • netw OS keeps command & processes it on behalf of DOS.
  • If command doesn’t involve a netw device (ex copy file from 1 dir to another on device C:), then netw OS gives command back to DOS for processing.
network request processing2
Network Request Processing
  • The netw OS does levels 3 to 6 as follows:
  • - It encrypts (codes) the file(L6)
  • - It sets up a communication session by(L5)
  • breaking the copy request into smaller packets
  • - It formats each small packet to detect transmission errors(L4)
  • - It does routing on a LAN:(L3)
  • -All packets (msjs) are transmitted to all nodes
  • -Each node reads msj adr & if for that node reads msj,
  • if not ignores msj
  • - It passes each formatted data block to the netw card for transmission on the network
distributed database processing
Distributed Database Processing
  • If the workgroup processes a database, then a multiuser DBMS is required.
  • 2 different architectures for processing databases on LAN:
  • resource - sharing
  • client/server
resource sharing database processing
Resource-Sharing Database Processing
  • Each comp has DBMS
  • & server operates as disk manager
  • (all processing is done on user comps
  • & server only provides complete tables of data )
client server database processing
Client-Server Database Processing
  • DBMS is divided into 2parts:
  • -client DBMS (on user comps,contains user interface)
  • -server DBMS (on server, does all db processing in response to requests from client DBMS)
  • Client DBMS & appl progs access server DBMS from client comps
adv of client server database processing
Adv of Client-Server Database Processing
  • 1. Requires only 1 copy of server DBMS
  • (client DBMS can be simpler & less expensive)
  • 2. Requires less transfer of data over LAN
  • (more data must be transmitted across LAN for resource-sharing)
  • 3. Provides better control of concurrent processing
  • (because a DBMS centralized on a single node provides this)
  • but permits less parallel processing
  • (i.e if 20 client PCs give requests to server at the same time, it affects server processing speed)
application programs in distributed systems
Application Programs in Distributed Systems
  • Types of application programs:
  • Horizontal application products:
  • - single-user versions
  • (ex: Lotus 1-2-3, Excel, Word, Word Perfect)
  • - multiuser versions
  • Vertical Application Products
  • (Custom developed applications by professionals)
single user application products
Single-user Application Products
  • - can run on networked comp w/o change.
  • If it uses local disk for storage/retrieval,
  • then can be unaware of network’s existance
  • - if it uses server for storage/retrieval, then user must use server device name
  • - but due to uncoordinated update activity, leaves workgroup open to errors & problems
multiuser application products
Multiuser Application Products
  • - provides features & functions for shared processing
  • - provides locks & other facilities to keep users from interfering w/ one another’s work
  • - when buying it must match network OS
application programs in distributed systems1
Application Programs in Distributed Systems
  • For Word or Excel to obtain data from group database on server,
  • it formats its request in away that the server DBMS can process
  • (ex: Excel provides a utility called Q+E to access data from SQL server)
  • Some types of data sharing are easy to accomplish (ex: e-mail)
  • but some other types create data management problems
  • (ex: 2 users editing changes on same doc)
  • Data for workgroup applications is usually shared :
  • - nonconcurrently
  • - concurrently
nonconcurrent data sharing
Nonconcurrent Data Sharing
  • Data can be shared w/out being processed simultaneously.
  • It can be done by:
  • - data partitioning
  • - processing partitioning
data partitioning
Data Partitioning
  • Data is divided into groups, each of which is processed by a single user.
  • Ex: account receivable dept processes past due accounts,
  • it can partition these accounts into groups by company name (1 account representative is assigned company names A to J, 2nd representative K to S, etc)
processing partitioning
Processing Partitioning
  • All the data is assigned to a single user for processing, but only for certain periods.
  • Ex: 1 user is authorized access to all data in the morning, & 2nd user in the afternoon
concurrent data sharing
Concurrent Data Sharing
  • Data can be shared by multiple users during the same time period
  • It is of 2 types
  • (depending on level of granularity):
  • - Record-level sharing
  • - File-level sharing
record level sharing
Record-level Sharing
  • 3 situations with record-level sharing:
  • 1. read/read
  • (2 users read the same record concurrently - no problem)
  • 2. read/update
  • (1 user reads, 2nd user updates same record concurrently -
  • inconsistent read problem)
  • 3. update/update
  • (2 users updating the same record concurrently, lost update problem)
read update inconsistent read problem
Read/UpdateInconsistent Read problem

User A tries to get total # of refrigerators in all Ws,

while user B is moving 3 refg from W1 to W2.

Follow the steps above & see how user A gets wrong total of refg.

update update lost update problem
Update/UpdateLost update problem

Follow the steps above & see how user A’s update is lost through

a problem in concurrent processing.

Note: changes made by 1st user are lost due to the update

made by the 2nd user

solution to concurrent sharing
Solution to Concurrent sharing
  • is record locking - records must be locked before they can be read for the purpose of update.
  • Record locking solves both
  • inconsistent read &
  • lost update problems,
  • but gives the problem of deadlock.

User A & user B are each processing orders for a diamond necklace & a black velvet box.

Follow the steps above & see how A & B have each blocked the other from completing their processing

(Resolving deadlock requires a commit/rollback technique - ie canceling one of the order transactions & starting it over after the conflicting order is completed)

file l evel sharing
File-Level Sharing
  • Is the file level of granularity, where monolithic files are shared across the workgroup.
  • - files such as word processing, spreadsheets, publications,& graphic images
  • - these files are nonstructured and noncoded
file l evel sharing1
File-Level Sharing
  • There are facilities for controlling such sharing
  • in the network OS
  • & in most multiuser products
  • Some programs dont have such capabilites, so user supplements this program control for sharing w/ manual procedures.

(if user states that a file is not to be shared,

the network OS won’t allow anyone to share it)

(A word processor locks doc file as nonshareable

when someone is editing the doc)

  • When programs do not provide facilities for coordinated access,
  • procdures need to be developed to coordinate the processing of workgroup members.
4 categories of procedures
4 Categories of Procedures

User’s need procedures for :

Operations personnel need procedures for :