PROGRAMS

1. PROGRAMS • The categories of programs for workgroup information systems are • system programs, including OS utilities, • DBMS, & • applications programs • (same as personal information systems)

2. 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.

3. 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

4. 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.

5. 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

6. 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

7. 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 )

8. 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

9. 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)

10. 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)

11. 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

12. 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

13. 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)

14. DATA • 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)

15. DATA • Data for workgroup applications is usually shared : • - nonconcurrently • - concurrently

16. Nonconcurrent Data Sharing • Data can be shared w/out being processed simultaneously. • It can be done by: • - data partitioning • - processing partitioning

17. 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)

18. 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

19. 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

20. 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)

21. 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.

22. 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

23. 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.

24. 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)

25. 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

26. 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)

27. PROCEDURES • When programs do not provide facilities for coordinated access, • procdures need to be developed to coordinate the processing of workgroup members.

28. 4 Categories of Procedures User’s need procedures for : Operations personnel need procedures for : backup