1. Middleware and ORB CS 314 Operating Systems
Department of Computer Science
Southern Illinois University Edwardsville
Spring, 2019
Dr. Hiroshi Fujinoki
Middleware/001

2. motivation for middleware
CS 314 Operating Systems
What is “middleware”?
“Middleware is a general term for any programming that serves to "glue
together" or mediate between two separate programs.”
The two separate programs are “user applications” and “operating systems”
for most middleware
The primary motivations for middleware
 To provide more complex and high-level services to a computer system
without increasing OS kernel size
This was the primary
motivation for middleware
in the mid 80’s.
 To provide more complex and high-level services to user application
programs without dependent on particular OS
 Glue different existing software systems together without
applying any modification to them
Middleware/002

3. (application-mode process)
CS 314 Operating Systems
What is “middleware”?
Application Program
(application-mode process)
API Call
System Call
Operating System
Middleware/003

4. (application-mode process)
CS 314 Operating Systems
What is “middleware”?
Without Middleware
Operating System
Application Processes
With Middleware
Operating System
Application Program
(application-mode process)
API Call
System Call
API Call
System Call
API Call
System Call
Complex
& Large
Middleware/004

5. CS 314 Operating Systems What is “middleware”? User Applications
Used (directly)
by Whom?
Execution Mode
(USER or KERNEL)
Purposes
OS-Dependent?
User Applications
(and Middleware)
Human Users
User applications
USER Mode
USER Mode
KERNEL Mode
Provide complex services
to user apps
Facilitator & Government
To get human-users’
jobs done
Interface to HW
User apps will be OS
independent
Resource Manager
(Resource Allocater)
YES NO
YES
Middleware/005

6. CS 314 Operating Systems What is “middleware”? With Middleware
Application Processes
 Distributed System
 Web
 Database
RPC
(Remote Procedure Call)
ORB
(Object Request Broker)
API Call
MOM
(Message-Oriented M.W.)
XML
System Call
Web servers
API Call
DBMS (Oracle Database, DB2, SQL Server,
MySQL, PostgreSQL)
Operating System
Middleware/006

7. CS 314 Operating Systems
Middleware/003

8. CS 314 Operating Systems Local Procedure Call (Ordinary Function Call)
main
ABC   
void main (void) { }
The callee
blocks here 
call ABC  
S = ABC(X, Y, Z);
int ABC(int X, int Y, char Z) { }
(1) Callee and caller have same data format
Large/little endian
7/8-bit ASCII codes
Text-line termination (CR+LF or CR)
32-bit or 64-bit integer
return(P);
(2) Two parameter-passing methods available
“pass-by reference/value”
(3) Low-latency turnaround
Middleware/007

9. CS 314 Operating Systems Remote Procedure Call (RPC) as a middleware
CLIENT
SERVER
void main (void) { }
int ABC(int X, int Y, char Z) { }
return(P);
S = ABC(X, Y, Z);
int ABC(int X, int Y, char Z) { }
return(P);
Network
Middleware/008

10. CS 314 Operating Systems Remote Procedure Call (RPC) as a middleware
LPC
RPC
Data Format
Parameter Passing
Low-Latency
Turnaround
Always same
Can be different
(between a calling
and a called function)
Pass-by Reference
Pass-by Value
Pass-by Value ONLY
(between a calling
and a called function)
YES NO
Middleware/009

11. CS 314 Operating Systems Remote Procedure Call (RPC) as a middleware
Data Marshaling
Construct a message
for transmission MW MW
CLIENT
Call OS (for Tx)
SERVER
RPC (C)
CLIENT
OS (C)
OS (S)
RPC (S)
SERVER
Wait (block)
main
RABC
The callee
blocks here
RPC(C)
blocks here
RPC(S)
blocks here
call RABC
Middleware/010
Weakness of RPC: No object-oriented programming supported

12. CS 314 Operating Systems Object Request Broker (ORB) as a middleware
CORBA = Common Object Request Broker Architecture
CORBA is a foundation where distributed objects (objects = functions)
are identified, called and expected to perform specific tasks.
This client has no
idea where this
request will be
executed
Concept
Client
Server
Function A
(Object A)
Program
Request
Request
Reply
Reply
Server
Function B
(Object B)
Broker
The broker finds
the best server
who can handle
this request
Middleware/011

13. CS 314 Operating Systems Object Request Broker (ORB) as a middleware
area(circle, int) { }
area(square, float)
area(circle, float)
area(square, int)
Polymorphism
Server C
Server D
Client
Program
Server A
call “area(circle, 9.54)”
Request
Request
Reply
Reply
Broker
The broker finds
the best server
who can handle
this request
Server B
Middleware/012

14. CS 314 Operating Systems Object Request Broker (ORB) as a middleware
area(circle, int) { }
volume(circle, float) { }
Inheritance
area(circle, 9.54)
Server C
Server D
Client
Program
Server A
call “volume(circle, 9.54)”
Request
Request
Reply
Reply
Broker
area(circle, float) { }
The broker finds
the best server
who can handle
this request
Server B
area(square, int) { }
Middleware/013

15. CS 314 Operating Systems Object Request Broker (ORB) as a middleware
area(circle, int) { }
volume(circle, float) { }
Inheritance
area(circle, 9.54)
Server C
Server D
Request
Reply
Client
Program
Server A
call “volume(circle, 9.54)”
Request
Reply
Broker
area(circle, float) { }
The broker finds
the best server
who can handle
this request
Server B
area(square, int) { }
Middleware/014

16. CS 314 Operating Systems Before CORBA was introduced
Web Server
Web Contents
Company’s Web Site
To the Internet
Database
Server
Database
Server
Customer Profile
Service
Seat Reservation
Service
Middleware/015

17. CS 314 Operating Systems Without CORBA ….
1. Since each system is independent, different systems must be used
for each different task
2. Applications in different systems can not easily communicate each other
3. Hardware resources are not efficiently utilized (results of the above two)
Middleware/016

18. CS 314 Operating Systems Before CORBA was introduced
Company’s Web Site
Web Server
Web Contents
To the Internet
Server
Database
Customer Profile
Service
Server
Database
Seat Reservation
Service
Customer (or user)
Middleware/017

19. CS 314 Operating Systems After CORBA was introduced CORBA Broker
Company’s Web Site
Web Server
Web Contents
To the Internet
ORB
CORBA Broker
Server
Database
Customer Profile
Service
Server
Database
Seat Reservation
Service
Middleware/018

20. CS 314 Operating Systems After CORBA was introduced CORBA Broker
Company’s Web Site
Web Server
Web Contents
Customer
To the Internet
ORB
CORBA Broker
Server
Database
Customer Profile
Service
Server
Database
Seat Reservation
Service
Middleware/019

21. CS 314 Operating Systems CORBA Connectivity through HTTP
Example: Integrated Information System by American Airlines (
Middleware/020

22. CS 314 Operating Systems
Middleware/021

23. CS 314 Operating Systems Client Stub A client stub is a proxy object
Host A
CORBA Client Process
Local object call
Remote object call
through CORBA
local
object
ORB
Network
as a middle-wear
remote
object
ORB
Host B
Middleware/022

24. CS 314 Operating Systems Host A CORBA Client Process Skeleton ORB ORB
local
object
Host A
Local object call
ORB
Remote object call
through CORBA
client
stub
CORBA Client Process
remote
object
ORB
Skeleton
Host B
remote
object
ORB
Network
Middleware/023

25. CS 314 Operating Systems
CORBA Time Server and Client Overview (continued)
Time Client
Time Server
Time Client
CORBA program
Time Server
CORBA program
Current_Time();
11:01:58
Current_Time();
As a
Middleware
CORBA Interface
(IDL)
ORB
IIOP
TCP/IP OS
Internet
Middleware/024

26. CS 314 Operating Systems                       
Comparisons with other distributed technologies            
Issues
Socket
RPC
CORBA
Distributed computing
Hardware Independence
OS Independence
Language Independence
Locational Transparency
Abstraction Level
Overhead       
Middleware/025

27. CS 314 Operating Systems What is “CORBA” (continued) ?
CORBA is not a product, but a specification for ORB (Object Request Broker)
Major products for CORBA*1:
Orbix
OmniCORBA (one of free CORBA distributions)
Sun’s Java IDL
ILU (The Inter-language Unification project from XEROX)
CorbaPlus for C++
CORBA specification is established and managed by OMG
(OMG = Object Management Group*2)
*1: A list of CORBA products available at
*2: OMG Web Site:
Middleware/026

28. CS 314 Operating Systems
OMG (Object Management Group)
Middleware/027