Download N-tier Architectures: Evolution of Enterprise Computing Systems and more Study notes Architecture in PDF only on Docsity!
N-tier Architectures
DB3 - 2005
In this section…
Iadh’s been blasting you with SQL to a highstandard!
Look at applications of SQL in programminglanguages, in particular
JDBC, SQLj
PHP
Also other crucial aspects of data intensive systems
transactions
First, though, in this lecture
attempt to fit all this in context – Enterprise computing
DB3 - 2005
What characteristics do we wantour Software to have (PSD…?)?
Easily Developed
Speedily Developed
Agile
Easily Understood
Easily Maintained
Easily Modifiable
Reliable
DB3 - 2005
Major components inEnterprise computing
Basically
data
business logic
interfaces
But this can be/is implemented in more layersoften.
DB3 - 2005
The Mesozoic Era The dinosaurs and the mammals appeared during the Triassic period,roughly 225 million years ago. The dinosaurs went extinct 65 million years ago
DB3 - 2005
Computer Systems Timeline
Monoliths
Client Server
Period
3 tier
Period
N-tier
Period
Legacy Era
Component-Based
Era
NOW
Web Services
Era
DB3 - 2005
In the beginning….
Enterprise
Salaries
Orders
Accounts
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Monolithic Era
Single chunks of code
Data Storage embedded
UI embedded
System rules embedded
No inter-system dependencies
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Addressing – the DNS
root
oz
uk
com
oz
uk
com
ac.ukco.uk
ac
co
gla.ac.uk
strath.ac.uk
gla.ac.uk
strath.ac.uk
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Client - Server
Client
Server
Address
Another
Server
sockets
Port
Port
Server Protocol
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Client - Server
Client
Server
Address
Another
Server
sockets
Another
Client
Server Protocol
Port Port
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Client-Server Era - Reasons
Advent of PCs
Availability of off-the-shelf DBMSs
Advent of RAD Tools
Acceptable networking facilities
Distributed Processing load across clients
Visualisation at the client level and dataprocessing at the server level
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Whence the business logic?
At the client?
Yes, usually – hence
Fat Client
Difficult to deal with maintenance and change
At the server?
Could store functions in the DBMS but itoverloads the server
The client and server are tightly coupled.
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Client-Server deficiencies
Difficult to reuse client with different datasources
Difficult to reuse server on different front-end
Development tools were poor
Developers were contaminated by themonolithic culture
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Developers’ myopia
No concept of separating out business logic
Focus on reuse OF CODE
The first generation tools were impressive topeople who had had
no
tools
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Next step?
Client-Server
Monoliths
?
DB3 - 2005
Server-Side Processing
Server
Component
Application Server
Server Machine
Monoliths
Client Server
Period
3 tier Period
N-tier Period
What is neededto make this runefficiently?
DB3 - 2005
Advantages of 3 tier
Loosely coupled
Agile Software
Use of pre-assembled parts
Promotes reuse of parts
Eases maintenance
Ease of versioning
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Interconnection?
Customised connection would be too difficult
Use standardised data bus like CORBA
So MxN connection is simplified to 1x1connection
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Data Bus Concept
Client
Server Object
Client
Object Request Broker
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
Limitations
Technical
Size of executable
Speed of execution
Cultural
Updating legacy systems to 3 tier is not alwaysacceptable to people used to monoliths
Monoliths
Client Server
Period
3 tier Period
N-tier Period
DB3 - 2005
What next?
Client-Server 2 tiers
Monoliths 1 tier
3 tiers
n tiers
DB3 - 2005
4 tiers…
Data
Business Logic
Web Server
Client
3 2 1
4
Monoliths
Client Server
Period
3 tier Period
N-tier Period
Why is this interesting?Why necessary?What’s not enough with3-tier?
DB3 - 2005
Legacy Systems
Enterprise
Server
Adaptor
Server
Client
network
Business
Logic
Business
Logic
Business
Logic
Legacy System
DB3 - 2005
Crucially…
Software architectures follow advances insystems architectures
Note
follow
Each new sys arch leads to a right mess initially –
exciting new functionality gained at terrible price
until enough experience
mindset changes among developers
development of truly innovative software structures
Software architectures – an ongoing rsch area
