1. Seminar „Web Services“
MIDDLEWARE
Wolfgang Gassler, Eva Zangerle

2. OVERVIEW introduction types of middleware RPC based systems
TP monitors
object brokers
object monitors
message oriented middleware

3. INTRODUCTION provide interface to integrate heterogeneous systems
manage interaction application <-> server
roles of middleware
as a programming abstraction
hide complexity to the programmer
as an infrastructure
basis of programming abstraction
extensions

4. RPC History How RPC works RPC binding RPC heterogeneity RPC extensions
RPC transparency

5. RPC - History RPC = Remote Procedure Call Birell and Nelson (1980s)
calling procedures on remote machines
basis for two tier systems
start of the developement of distributed systems
basis for middleware, EAI and web services

6. RPC – How it works I interface for procedures Compilation of IDL
IDL (Interface Definition Language)
Compilation of IDL
Result of compilation
client and server stub for every defined procedure
interface headers

7. RPC - IDL Compilation - result
development
environment
client process
server process
IDL
client code
IDL
sources
server code
language specific call interface
language specific call interface
IDL compiler
client stub
server stub
interface
headers

8. RPC – How it works II client process server process client server
procedure call
server
procedure
dispatcher
selects stub
server stub
(un)marshal
(de)serialize
receive (send)
client stub
locate
(un)marshal
(de)serialize
send (receive)
communication module
communication module

9. RPC - binding static binding hard coded stub simple efficient
not flexible
stub recompilation necessary if the location of the server changes
use of redundant servers not possible

10. RPC - binding dynamic binding name and directory server
load balancing
IDL used for binding
flexible
redundant servers possible

11. name and directory server
RPC - dynamic binding
client process
server process
client
procedure call
server
procedure 3 13 11 10
client stub
bind
(un)marshal
(de)serialize
find
send
receive
server stub
register
(un)marshal
(de)serialize
receive
send 8 1
communication module
communication module
dispatcher
selects stub 12 4 9 7 12 12 5 6 2
name and directory server

12. RPC - Heterogeneity RPC hides heterogeneity of a system
x servers, y clients
2*x*y stubs, for each combination
too much, not efficient
solution: common form of representation
mapped in IDL (platform independent)
x+y stubs need to be implemented

13. RPC - Extensions conventional RPC: sequential execution of routines
client blocked until response of server
asynchronous RPC – non blocking
client has two entry points(request and response)
server stores result in shared memory
client picks it up from there

14. RPC - Transparency
+ programmer aware of distribution, performance and reliability issues
+ error detection is easier
no need to worry about details
simplicity
less opportunities to cause errors

15. TP Monitors
History
Transactional RPC
How TP monitors work

16. TP Monitors TPM = transaction processing monitors
oldest form of middleware
most efficient and best tested middleware
basis for many new middleware platforms

17. TPM - History
Customer Information and Control System by IBM (late 1960s)
alternative operating system
complete development tool
later split up in modules
logging, recovery, persistence, security....
TP lite monitors
provide core functionality of TPM
embedded in database management system
result = two tier system

18. TPM – transactional RPC I
conventional RPC
not taking care of dependencies within various calls
difficult error detection
TRPC
derived from database transactions
transaction criteria: atomicity, consistency, isolation and durability
if not all criteria are fullfilled: rollback
criteria also applicable to RPC calls

19. TPM – transactional RPC II
define procedures within transactional brackets
„beginning of transaction“ – BOT
„end of transaction“ – EOT
handled by transaction management tool
responsible for interaction between client and server

20. TPM – transactional RPC
client process
server process
client
BOT
procedure call
EOT
server
procedure 1 4 9 10
client stub
register txn & create context
add txn id & context to call
request commit
confirm termination
server stub
extract context & txn id
register server for tx
participate 2PC 2 6 5 7 11 13 14 12
lookup txn id run 2PC notify client of outcome 3
create txn id register txn register client for txn return txn id 8
lookup txn id register server for txn
transaction manager

21. TPM – 2 phase commit protocol
„prepare to commit“ message to server
server responds „ready to commit“
guarantees successful commit of procedure
check whether all servers are ready
ready: commit results of requests
not ready: cancelation, rollback
log states of transactions

22. OVERVIEW III Object Brokers (CORBA) History CORBA System Architecture
How CORBA works
Dynamic Service Selection
Encapsulation
Object Monitors

23. Object Brokers - History
1990s – object oriented programming
similar to RPC
Problem: object oriented features
CORBA by OMG
Common Object Request Broker Architect.
DCOM / COM+ (Microsoft)

24. CORBA – System Architecture
Vertical facilitites
CORBA facilities
Financials
Health care
...
user-definied
objects
Horizontal facilities
Distributed
documents
Systems
management
Information
management
Task
management
Object Request Broker (ORB)
CORBA services
naming
transactions
events
lifecycle
properties
relationships
time
licensing
trader
concurrency
query
security
collection
startup
persistence

25. CORBA – How it works IDL of service provider application object
(client)
IDL compiler (client)
IDL compiler (server side)
application object (client)
application object (service provider)
stub
skeleton
Dynmic Invocation Interface
Object Request Broker (ORB)
Interface repository

26. Dynamic Service Selection
Dynamically discover new objects
Interface repository (stores IDL definitions)
Dynamic invocation interface
Naming and Trader services
In practice NOT used!
meaning of the properties, parameters?

27. Encapsulation Hides internal details Change implementation
Change programming language
Change platform/operating system
Change location (General Inter-ORB Protocol )

28. Object Monitors Extremely inefficient Lacked key functionality
Too long time for implementation
Object Monitors = TP Monitors + Object Brokers

29. Summary Object Brokers/CORBA
Object oriented
Provides many services
Difficult to handle/manage
Not used

30. OVERVIEW IV Message Oriented Middleware How it works Message Channels
Message Routers
Message Queues

31. Message Oriented Middleware
Asynchronous forms of interaction
Communication by exchanging messages
More dynamic

32. Message Oriented Middleware
Message : quoteRequest {
QuoteRefernceNumber: Customer: University of Innsbruck Item: #120 (IBM Laptop)
Quantity: 10 DeliveryAdress: Innsbruck }
client application
Message-Oriented Middleware (MOM)
Message : quote {
QuoteRefernceNumber: DeliveryDate: Nov 10, 2004
Price: EUR }
quotation tool

33. Message Queues client application server application MOM Core
queued messages
MOM Core
inbound queue

34. Shared Message Queues server application n client application
MOM Core
inbound queue

35. Summary Message oriented MW
Asynchronous
More dynamic
Flexibility
Modular
Often used in new projects

36. SUMMARY RPC based systems TP monitors object brokers object monitors
message oriented middleware

37. Seminar „Web Services“?
Seminar „Web Services“
MIDDLEWARE
Wolfgang Gassler, Eva Zangerle