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ISM 50 - Business Information Systems
Lecture 12
Instructor: John Musacchio
UC Santa Cruz
October 31, 2006
Announcements
Read Messerschmitt Ch 7 for Tuesday.
Presenters for Thursday
Zhuo H Yang (news)
Christy Kitmum Loke (news)
Database Tutorial Sessions
Student Talks
Devin Blann ( news)
George Numair (news)
Client-Server Architecture
(continued)
Client Server Example – Layers Revealed
Client
Application:
Infrastructure
Server
Google
3-Tier Client Server Architecture example
Application Server
Shared
data
Web Server
Application Logic
Common Gateway Interchange
Client
3-Tier Client Server Architecture example
Application Server
Shared
data
Web Server
Application Logic
Common Gateway Interchange
Client
Database Management System (DBMS)
What is Bob’s Balance?
Database
3-Tier Client Server Architecture example
Application Server
Shared
data
Web Server
Java Servlet
Client
Database Management System (DBMS)
What is Bob’s Balance?
Database
In some implementations Application Logic and Web Server can be put on Different machines.
Application Logic
Relational Database
Customer
Class
Customer Balance
Charles $1000000 Gold
Bob $0.50 Bronze
Alice $527 Silver
DBMS Responsibilities
Hide Changes in the Database hardware from the
Application
Standard operations on the data, including
searches, such a search is called aquery.
Separate Database Management from
Applications, so that many applications can access
the same data.
Security, Integrity, Backup, fault tolerance, etc..
3-Tier Client Server Architecture in General
Application Server
Shared
data
Client
-Accept instructions from user -Make requests of server -Display responses of server
-Takes inputs from client -Decides what to be done next -Decides what shared data to access and manipulates it -Processes shared data
-Support multiple applications with common data -Protect critical data -Decouple data administration and application administration
Sun N-tier Sun N-Tier
Sun’s Performance
(1,048.0)(2,653.0)(3,429.0)(3,429.0)1,121.21,176.21,605.72,771.01,584.01,031.31,854.0(587.0)(388.0)(106.0)1,031.31,854.0(587.0)(388.0)(106.0) 1,627.01,716.0(461.0) 523.3708.9437.0738.0355.8476.4762.4762.9981.0 (54.0) 355.8476.4762.4762.9927.0 (0.18)(1.07)(0.12)(0.03)(0.18)(1.07)(0.12)(0.03) 1995199619971998199920002001200220032004 378.0273.0200.0167.5232.5358.8413.3574.4917.0603.0776.0825.0844.0 31493147311131543256337834173242319032773378 TTM 22.933.994.746.183.971.00.110.150.250.240.320.550.290.110.150.250.240.320.550.27------------------------------------------------------------------------------------------------
Net Income 355.8 476.4 762.4 762.9 1,031.3 1,854.0 927.0 (587.0) (3,429.0) (388.0) (106.0)
Today
3-tier model common.
Sun’s version of 4-tier model not-common.
N-tier model where Webserver and
Application Server on separate equipment
also common.
Sun’s hardware business not strong.
Linux on cheap PCs most common servers
Microsoft desktops replacing Sun workstations
Today
Java
Common in Server implementations
Example: Java Servlet implementing application logic
in a banking application.
Often used to push simple applets onto client
Not common
For “big” desktop applications
Office Suite in Java not popular
Microsoft is still in business…
Architecture Example
Architecture
Conceptualization
What is it you are trying to do?
Example Concept:
Small HHC for flight attendants.
HHC tells flight attendants which passengers are higher
priority.
Who paid the highest fares Who has been a more valuable customer in past
Flight attendant discriminates based on this
Free drinks, meals, and pillows to valuable customers Ignore less valuable customers
Example Concept:
Architecture
How do you begin to architect a solution
for a problem like this?
Break it into modules!
Architecture
Airline Dataserver
HEADQUARTERS
HHC
HHC Server
Airline Intranet
Wireless Link
HHC Architecture
When a module is composed of sub-modules,
the architecture is hierarchical.
HHC Application
Palm OS
Networking Infrastructure
User Interface
Coordination With HHC Server
Data Management
HHC Architecture
We are using a layered architecture as well.
Allows reuse of previously built infrastructure.
HHC Application
Palm OS
Networking Infrastructure
User Interface
Communication With HHC Server
data management
Example data types
Integer
“natural number between -32,767 and +32,768”
Could be represented (in many ways) by 16 bits
since 2n^ = 65,
Float
“number of the formm*10n/32768, wherem is in the
range -32,767 to +32,768 andn is in the range -255 to
Could be represented by 16+8 = 24 bits
More data types
Character
“values assuming a-z and A-Z plus space and
punctuation marks”
could be represented by 7 or 8 bits
Character string
“collection ofn characters, wheren is
customizable”
could be represented by 7*n bits
Compound data types
Programmer-defined composition of basic
data types
Example:
Employee {
String name;
String address;
Integer year_of birth;
etc.
Interfaces
Computation of key statistics
N numbers of Float type
2 Numbers of float type that signify: Mean, Variance
Compute Mean and Variance
INTERFACE
PARAMETERS
RETURNS
Implementation
Computation of key statistics
Compute Mean and Variance
Implementation 1:
X^ i, i=1..N
MEAN, VARIANCE
One module should not be concerned with other module’s implementation Æ “Separation of concerns.” One module should see the other only through its interface – implementation details hidden. Æ Abstraction
Module A
Module B
HIDDEN From Module A!!
Implementation
Computation of key statistics
Compute Mean and Variance
Implementation 2:
X^ i, i=1..N MEAN, VARIANCE
Though different, this implementation is ok too.
We can choose the implementation details however we want, as long as we comply with the agreed interface.
Module A
Module B
Implementation
Computation of key statistics
Compute Mean and Variance
Implementation 1:
X^ i, i=1..N MEAN, VARIANCE
Should he use it?
NO!!!! Why??
Either A should compute “SUM” himself, or
sit down with B and redesign the interface
Module A
Module B
“I need to get the sum, I’ll just take it from B”
Encapsulation
The designer of B might take measures to
hide “SUM” from A so that A is not able to
violate the agreed interface.
Example: B does not declare “SUM” as a global
variable.
Making a modules implementation details
inaccessible to other modules is called
encapsulation.
Interfaces
Computation of key statistics
N numbers of Float type
2 Numbers of float type that signify: Mean, Variance
Compute Mean and Variance
INTERFACE
PARAMETERS
RETURNS
This simple interface example allows for only one action of module B. Action is “Compute mean and variance.”
Other examples are possible.
Module B
Module A
Possible software interface
action-
action-
action-
Menu of actions
Action 1: Compute mean
Action 2: Compute variance
Action 3: Compute mode
Etc..
Example:
Protocol
In addition to atomic actions, an interface
may define protocols
Protocol == finitesequence of actions required
to achieve a higher level function
One action can be shared by multiple protocols
Multiple modules may participate in a protocol
Protocol Example
HHC Server
HHC
Hello: I’m the gate 32 server
Hello: I’m the HHC of Airplane#
Tell me about the passengers of my next flight
Return Weather Data
(Might be passed As an array of a compound data type “passenger,” which in turn is composed of standard types like integer, and string)
Tell me about the weather at my next destination.
Return Passenger Data
“Passengers noted”
These were the unruly passengers on last flight
Action: specify_account
Parameters
Account (touch screen from menu of choices)
Internally, choice noted for all subsequent
actions (another example of state)
Returns
None
Action: amount
Parameters
Dollars_and_cents (typed on keypad)
Internally, amount noted (another example
of state)
Returns
Success or failure (state dependent, for
example for a withdraw failure when
dollars_and_cents exceeds balance)
Protocol: cash_withdrawal
What is the sequence of actions?
Protocol: cash_withdrawal
authentication
choose objective
account
amount
failure
other objectives
no accounts
balance exceeded!
More on layering
by
David G. Messerschmitt
Goals
Understand better
how layering is used in the infrastructure
how it contains complexity
how it coordinates suppliers
how it allows new capabilities to be added
incrementally
Layer above is a client of the
layer below
Layer below as as a server
to the layer above
….by utilizing the services of the layer
below and adding capability
Each layer provides services
to the layer above….
Interaction of layers
Application module Application module
Host A Host B
Middleware
Operating system Operating system
Network
Middleware
Layering
Existing layers
Elaboration or specialization
Ú Ú Ú
Layering builds capability
incrementally by adding to what
exists
Three types of software
Application
•Infrastructure:
Basic services (communication, storage,
concurrency, presentation, etc.)
•Components and frameworks:
What is in common among applications
Part of Microsoft vs. DOJ
dispute
Application
Infrastructure
Components and frameworks
Microsoft
position
DOJ
position
Network
Operating system
Middleware
Application frameworks and components
Applications
Major layers
Example 3
HHC
HHC Server
HHC Server Application HHC Client Application
Passenger Information
Windows OS
message
Networking Infrastructure (Contains: TCP/IP, WiFi)
Collection of Packets (^) Networking Infrastructure (Contains: TCP/IP, WiFi)
Palm OS
message
Example 3: Network Infrastructure Expanded
HHC Server Application HHC Client Application
Passenger Information
Windows OS
message
TCP transport layer
Palm OS
message
WiFi Link Layer
Packets
WiFi Physical Layer
Networking Infrastructure
TCP transport layer
WiFi Link Layer
Packets
WiFi Physical Layer
Networking Infrastructure
Radio Signals
Example 4
HHC Server
HHC Server Application DBMS
Windows OS
message
Networking Infrastructure Layers within TCP/IP, WiFi
Collection of Packets (^) Networking Infrastructure Layers within: TCP/IP, WiFi
Unix OS
message
Airline Dataserver
HEADQUARTERS
“Send me today’s flight information”
Information in the
infrastructure
Sometimes it is appropriate for the
infrastructure to assume structure and
interpretation for data
to add capabilities widely useful to applications
to help applications deal with heterogeneous
platforms, where representations differ
At most, data types
Data and information
Application
Deals with information
Infrastructure
Deals with data types
Assumes structure and interpretation
Assumes standard data types
