Transcript Technologies

Technologies
For use on different layers
Technologies
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Client tier
Client tier to middle tier protocols
Middle tier technologies
Middle tier to data tier technologies
But first…what is a protocol?
• ‘In computing, a protocol is a convention or
standard that controls or enables the
connection, communication, and data transfer
between two computing endpoints. In its
simplest form, a protocol can be defined as the
rules governing the syntax, semantics, and
synchronization of communication. Protocols
may be implemented by hardware, software, or
a combination of the two. At the lowest level, a
protocol defines the behaviour of a hardware
connection.’ – www.wikipedia.org
Wikipedia.org…
• Protocols are generally used to define real-time
communications behaviour. Most protocols specify one
or more of the following behaviours:
– Detection of the underlying physical connection (wired or
wireless), or the existence of the other endpoint or node
– Handshaking
– Negotiation of various connection characteristics
– How to start and end a message
– How to format a message
– What to do with corrupted or improperly formatted messages
– How to detect unexpected loss of the connection, and what to do
next
– Termination of the session or connection
Client tier
• Client applications
– Human to human communications:
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E-mail, instant messaging, USENET news, chat.
File transfer or file swapping.
Remote login.
Proprietary applications (e.g. a multi-user game).
– Clients hosted in a Web browser can use the
following:
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HTML forms.
JavaScript.
Proprietary plug-ins (e.g. Flash).
ActiveX controls.
Java applets.
Client tier protocols
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IMAP for e-mail
AIM for instant messaging
HTTP/CGI for HTML forms
Browser Apps and plug-ins can be written
in:
– Java, C++, Eiffel, Fortran, even Cobol.
– Need a compiler for your chosen language
that will put the code into a DLL (MS
Windows) or shared library (UNIX).
HTML
• Visually rich and widely supported.
• Forms are primitive and not automatically
validated on the client.
• Not visually pleasing ( step through pages,
each of which flashes white before it is
drawn).
JavaScript
• Permits some programming on the client
side.
– E.g. data validation.
• Interpreted, so slower than compiled code.
• Not purely object-oriented.
• Different browsers provide different levels
of support.
Plug-ins and ActiveX
• Plug-Ins
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Can provide client interaction.
Need to be downloaded and installed.
Each one requires different programming expertise.
Must be ported by supplier to each new platform.
• ActiveX controls
– These are 32-bit Windows binaries, hosted by a web
browser. They can only run on Windows.
– Controls such as clocks and calendars can be added
to forms.
Java and new clients
• JAVA
– Simple
– Pure object-oriented language.
– Prohibits access to resources on the local machine
without user authorisation.
• New clients
– Mobile phones
– PDAs (Personal Digital Assistant)
– Most of the technologies have a version for these.
Client tier to middle tier protocols
• Communicates between the client and the
server.
• Layered:
– At the bottom, TCP/IP
– SSL (Secure Socket Layer) which encrypts and
decrypts information for privacy and integrity (optional
layer).
– Secure HTTP (HTTPS), allowing a client to request a
document by URI and get back the contents of that
document (e.g. Squirrelmail) (optional layer).
– JRMP (Java Remote Method Protocol) allows Remote
Method Invocation (RMI), allowing an object to send a
method to a remote object.
How RMI can use a network
aClient
aServant
JRMP
HTTPS (Optional)
SSL (Optional)
TCP/IP
After O’Docherty, M.,’Object-Oriented Analysis and
Design’, p245, Wiley, 2005
Continued…
• Commonly used protocols can be specialised and
general:
• Specialised:
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IMAP (e-mail)
AIM (AOL Instant Messaging)
NNTP (USENET news)
HTTP / CGI (HTML forms)
FTP (File transfer protocol)
Telnet (remote login)
• General:
– TCP/IP (low level transport, also known as sockets)
– JRMP (for Java-to-Java communications)
– IIOP (for CORBA communications
• Like RMI, but lots of different languages.
Middle tier technologies
• This tier (layer) is reached when the
user’s interaction with the system is
accepted and has been passed on to a
server.
• Server applications may be multi-threaded
and designed for high capacity.
• A server application ‘listens’ to a port
(connection point) for clients to connect.
• Applications can be stand-alone or can be
run from a web-server.
Stand-alone applications
• Mail, messaging, news, chat servers.
• FTP daemon
– A daemon is a type of housekeeping task, that is used by the
operating system in a multitasking environment, to ensure that
all tasks are properly initiated and ended.
• Telnet daemon
• Naming services
– These allow clients to find the server object by name E.g.:
• CORBA registry
• RMI registry or
• Java Naming and Directory Interface (JNDI) server ( a general
name-to-thing mapping service)
• Proprietary server (e.g. a process hosting CORBA or
RMI objects, an EJB client or a .NET client).
Server code
• Hosted by a web server:
– JSP (Java Server Pages) for building Web pages.
• Raw HTML interspersed with Java code.
– ASP (Active Server Pages) (VB version)
– CGI scripts
• Textual files written in a command language (e.g. PERL –
usually invoked by HTML)
– Servlets (Java server objects that are instantiated on
demand by applets, JSPs or HTML forms).
Middle tier to data tier technologies
• To access the data tier, either:
– Include database-client code on the middle tier, sot
we can access a DBMS running on the data tier (e.g.
using Java and JDBC (Java Database Connectivity))
– Use same protocols as for client-to-middle tier
– Use some non-TCP/IP protocol (legacy system)
– Include Enterprise Java Beans (EJB) client code in
our middle-tier server and access the data tier via
EJBs (see next slide)
– Include .NET code in the middle tier server. (Microsoft
version of EJB)
Enterprise JavaBeans
• The Enterprise JavaBeans (EJB) specification is one of the
several Java APIs in the Java Platform, Enterprise Edition.
• EJB is a server-side component that encapsulates the business
logic of an application. The application server provides:
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persistence
transaction processing
concurrency control
events using Java Message Service
naming and directory services (JNDI)
security
deployment of software components in an application server
• remote procedure calls using RMI-IIOP or CORBA
• Additionally, the Enterprise JavaBean specification defines the roles
played by the EJB container and the EJBs as well as how to deploy
the EJBs in a container.
– Wikipedia.org
How they fit together
Middle
Client
IMAP, AIM, NNTP, IRC, FTP, TELNET, HTTP, TCP/IP, JRMP,I...
preemptive
Messaging
News
Mail
Internet Relay Chat
File transfer tool
Remote login (Telnet)
Proprietary tool
Web browser
HTML/CGI
Plug-in
Applet
Propretary DB protocol, JDBC net, IIOP, JRMP, TCP...
DataLayer
DBMS
JDBC net server
Database client
Proprietary data server
EJB data source
Mail Server
Messaging server
Internet Relay chat server
File transfer daemon
rlogin/telnet daemon
Proprietary server (Corba/RMI/EJB)
JNDI server
CORBA naming service
Web server
Client
preemptive
Messagi ng
News
Mail
Internet Relay Chat
Fil e transfer tool
Remote login (Telnet)
Propri etary tool
Web browser
HTML/CGI
Plug-i n
Appl et
Client tier
Middle tier
Middle
Mail Server
Messaging server
Internet Relay chat server
Fil e transfer daemon
rl ogi n/tel net daemon
Propri etary server (Corba/RM I/EJB)
JNDI server
CORBA naming service
Web server
DataLayer
DBMS
JDBC net server
Database client
Propri etary data server
EJB data source
Data tier