TIM 50 - Business Information Systems - University of ... 50 - Business Information Systems Lecture...

TIM 50 - Business Information Systems

Lecture 10

Instructor: Ram Akella

UC Santa Cruz

February 20, 2017

Class Announcements

Architecture

n How do you begin to architect a solution for a problem like this?

n Break it into modules!

n New in-flight seatback systemn Sell upgrades and seat swaps

n (People who want to get away from sick people …)q More legroom q Offer to exchange seats

Architecture

Airline Dataserver

HEADQUARTERS

Wireless Link

Seat back devices

servers

Wireless Link

Seatback Architecture

When a module is composed of sub-modules, the architecture is hierarchical.

Seatback Application

Linux OS

Networking Infrastructure

User InterfaceCoordination

With On Plane Server

Data Management

HHC Architecture

Seatback Application

Linux OS


User InterfaceCoordination

With On Plane Server

Data Management

• We also make use of layers

Granularity tradeoff.

n How big should we make the modulesq Many simple small onesq Or a few complicated big ones…

n This aspect of modularity is called granularity.

n Which is better?

In-plane Server

n Again, we see layering and hierarchy.n Between each module we specify an interface


LinuxOS

Server Application

Communicationwith airlinedatabase

Computationof key statistics

CommunicationWith seat backs

Standard Database “queries” (SQL) relayed to DBMS via OS and infrastructure

Data server

Database

DBMS

Standard Database “queries” (SQL) from HHC Server

Our architecture makes use of theExisting interface of the airline database,so we don’t need to redesign it!

A simple interface: from within Architecure

HHC Application

Linux



Communicationwith HHC

Communicationwith airlinedatabase


Compute Mean andVariance

Mean,Variance

List of numbers

Interfaces

Interface specifications are often made precise by using data types.

n Example type: floatq A number with a decimal placeq Has a certain allowable range, and precision.


N numbers ofFloat type

2 Numbers of float type that signify:Mean, Variance


More on Data types

n Data passing an interface is often specified in terms of a limited number of standard data types

n Data type = range of values and allowable manipulation

n Data type does not presume a specific representation, to allow heterogeneous platformsq Representation must be known when data passes a

specific module interface

Example data types

Integerq “natural number between -32,767 and +32,768”q Could be represented (in many ways) by 16 bits

n since 2n = 65,536

Floatq “number of the form m*10n/32768, where m is in the

range -32,767 to +32,768 and n is in the range -255 to +256”

q Could be represented by 16+8 = 24 bits

More data types

Characterq “values assuming a-z and A-Z plus space and

punctuation marks”n could be represented by 7 or 8 bits

Character stringq “collection of n characters, where n is

customizable”n 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





INTERFACE

PARAMETERS

RETURNS

Implementation



Implementation 1:

n One module should not be concerned with other module’s implementationq à “Separation of concerns.”

n One module should see the other only through its interface –implementation details hidden.q à Abstraction

Module A

Module B

HIDDEN From Module A!!

Implementation



Implementation 2:

n Though different, this implementation is ok too.

n We can choose the implementation details however we want, as long as we comply with the agreed interface.

Module A

Module B

Implementation



Implementation 1:

n Should he use it?q NO!!!! Why??

n 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

n The designer of B might take measures to hide “SUM” from A so that A is not able to violate the agreed interface.

q Example: B does not declare “SUM” as a global variable.

n Making a modules implementation details inaccessible to other modules is called encapsulation.

Interfaces





INTERFACE

PARAMETERS

RETURNS

n This simple interface example allows for only one action of module B. q Action is “Compute mean and variance.”

n Other examples are possible.

Module B

Module A

Possible software interface

action-1

action-2

action-3...

Menu of actions

Action 1: Compute meanAction 2: Compute varianceAction 3: Compute mode

Etc..

Example:

Protocol

In addition to atomic actions, an interface may define protocolsq Protocol == finite sequence of actions required

to achieve a higher level function

q One action can be shared by multiple protocols

q Multiple modules may participate in a protocol

Protocol Example

HHC ServerHHC

Hello: I’m the gate 32 server

Hello: I’m the HHC of Airplane#1234

Tell me about the passengers of my next flight

Return WeatherData

(Might be passedAs an array of a compound data type “passenger,” which in turn is composed of standard types like integer, and string)

Tell me about the weatherat my next destination.

Return PassengerData

“Passengers noted”

These were the unrulypassengers on last flight

Another Interface Example: Automatic teller machine (ATM)

What is the interface between this machine and the customer?

Steps

Define available actionsDefine, for each higher level function, a

protocolq Single action or a finite sequence of actions

Interface building blocks

Message on screen or printedq Menu of actions or returns from an actionq Touch selection of action

Keypadq Input parameters to an action

Card readerq Authentication, input parameters

Money output slotq Returns money

Action: authentication

ParametersInternal functionalityReturns

Action: authentication

Parametersq Identity (card in slot)q Institution (card in slot)q PIN (typed on keypad)

Internally, it contacts institution and matches against its database, institution noted for all subsequent actions (example of state)

Returnsq Screen message (“Invalid PIN” or menu of available

actions)

Action: specify_account

ParametersInternal functionalityReturns

Action: specify_account

Parametersq Account (touch screen from menu of choices)

Internally, choice noted for all subsequent actions (another example of state)

Returnsq None

Action: amount

Parametersq Dollars_and_cents (typed on keypad)

Internally, amount noted (another example of state)

Returnsq 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

byDavid G. Messerschmitt

Goals

Understand better q how layering is used in the infrastructureq how it contains complexityq how it coordinates suppliersq how it allows new capabilities to be added

incrementally

Layer above is a client of thelayer below

Layer below as as a serverto 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➴ ➴➴

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

Microsoftposition

DOJposition

Network

Operating system

Middleware

Application frameworks and components

Applications

Major layers

Data and information

ApplicationDeals with information

InfrastructureDeals with data

Assumes structure and interpretation

Ignores structure and interpretation

Data and information in layers

n The infrastructure should deal with data,q or at most minimal structure and interpretation

n The application adds additional structure and interpretation

n This yields a separation of concerns

Package = file, message

In the simplest case, the infrastructure deals with a package of data (non-standard terminology)q collection of bitsq specified number and ordering

The objective of the infrastructure is to store and communicate packages while maintaining data integrity

File for storage, message for communication

Data integrity

Retain theq valuesq orderq number

of bits in a package

Example 1

Bob Alice

Bob sends a letter to Alice

US Postal Service UK Royal Mail

ABC Airlines

Envelope

Shipping ContainerShipping Container

Envelope

Web browser

File systemOperatingsystem

File

Network

Message

Collection of packetsFragmentation Assembly

Message

HTML

Screen

Application

Web server

Example 2

Web page

Example 3

HHCHHC Server

HHC Server Application HHC Client ApplicationPassenger Information

Windows OS

message

Networking Infrastructure(Contains: TCP/IP, WiFi)

Collection of Packets Networking Infrastructure(Contains: TCP/IP, WiFi)

Palm OSmessage

Example 3: Network Infrastructure Expanded

HHC Server Application HHC Client ApplicationPassenger Information

Windows OS

message

TCP transport layer

Palm OS

message

WiFi Link Layer

Packets

WiFi Physical Layer


TCP transport layer

WiFi Link Layer

Packets

WiFi Physical Layer


Radio Signals

Example 4

HHC Server

HHC Server Application DBMS

Windows OS

message

Networking InfrastructureLayers within TCP/IP, WiFi

Collection of Packets Networking InfrastructureLayers within: TCP/IP, WiFi

Unix OSmessage

Airline Dataserver

HEADQUARTERS

“Send me today’sflight information”

Information in the infrastructureSometimes it is appropriate for the

infrastructure to assume structure and interpretation for dataq to add capabilities widely useful to applicationsq to help applications deal with heterogeneous

platforms, where representations differ

At most, data types

Data and information

ApplicationDeals with information

InfrastructureDeals with data types

Assumes structure and interpretation

Assumes standard data types

TIM 50 - Business Information Systems - University of ... 50 - Business Information Systems Lecture...

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