Design of Distributed Systems
Programming of Interactive Systems
Lecture 3
Fredrik Kilander
Wei Li
Agenda
• RMI
• Jini (Dynamic Service Discovery)
• Overlay Networks
– Web naming scheme
– Data Representation (XML)
• Web Service
• System Architecture
• Perspectives on interactive systems
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Binding a Client to a Server
2-15
Endpoint= IP+Port
(server, endpoint) pairs
Client-to-server binding in DCE
(distributed computing environment 1990-)
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Java RMI
• Clients get the service location directly
from the registry
• RMI Registry is known to both RMI Client
and RMI Server
http://download.oracle.com/javase/tutorial/rmi/TOC.html
RMI Registry
2
Lookup
stub
3
1
5
Client
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stub
4
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Register
(Service
Binding)
Service
stub
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Passing Object by Value or Reference
(RMI)
• The object to send to another
machine has to be Serializable.
Machine C
MP3Selector
Skeleton
Interface Method:
void Play();
void Play (String filename);
void Play (MP3Selector mps);
Machine A proxy2
MediaPlayer
Controller
proxy1
• The object to send has to have
the class definition in the
classpath of the receiving side
• Setup security policy file
Machine B
Skeleton
Media
Player
Interface Method:
void Play ();
void Play (String filename);
void Play (MP3Selector mps);
“http://myhost/a.mp3”
Three cases:
1) Play () without parameters. // only method name will be sent
2) Play (“http://myhost/a.mp3”) // send filename as a copied object (value/copy)
3) Play (mps) {
// send the copy of proxy2
play(mps.getLatestMP3())
// (reference to MP3Selector)
} http://java.sun.com/developer/onlineTraining/rmi/RMI.html
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Java Jini
• Jini is a technology for building service-
oriented architectures.
• Jini defines a programming model which
exploits and extends Java technology.
• Jini is a generally stable, fault-tolerant,
scalable, dynamic, and flexible solution.
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Java Jini
• Services discover lookup servers and
register with multiple properties
• Clients discover lookup servers and query
them for services
• Discovery with multicast (LAN) or unicast
(WAN)
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Java Jini
•
•
•
•
•
•
RMI: registry is co-located with the service
Jini: lookup services can be anywhere
RMI: client must know the registry host
Jini: clients discover lookup services
RMI: service found by name
Jini: service found by name, attributes and
interfaces
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Jini
Two ways to connect to a Lookup Service:
• Multicast to discover local lookup services
automatically (i.e. previously unknown)
• Unicast to connect to a lookup service on a
known host (e.g., remote subnet)
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Jini
Two ways to connect to a Lookup Service:
• Multicast (1-M) to discover local lookup
services automatically (i.e. unknown)
• Unicast (1-1) to connect to a lookup service
on a known host (e.g. on a remote subnet)
Multicast
Client
Local
Area
Network
Firewall
Internet
Lookup
service
Lookup service
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Jini (Registering a Service)
(1) Multicast/Unicast
to discover the LUS
(2) Retrieve a registrar
object from the LUS
(3) Use registrar to send a
service object to the LUS
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Jini (Discover a service)
(1) Multicast/Unicast to connect to LUS
(2) Retrieve a registrar object from LUS
(3) Search service using registrar
(4) Retrieve a service object (proxy)
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JINI
2) Dynamic Service
Discovery:
1) Simplified Running
Environment:
• Multicast to discover local
lookup service automatically
• Only one Jini lookup service is
necessary in a local Jini
network (local subnet). RMI
and RMIRegistry is optional.
(Lookup
Service)
• Unicast is used for a
service to register from a
remote subnet
(2)
(4)
(1)
(3)
(5)
http://jan.netcomp.monash.edu.au/java/jini/tutorial/Jini.html
http://www.jini.org
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Jini distributed garbage collection
• Leases (time-delimited promises)
• Example:
– A service registers a service object on the
lookup server in return for a lease
– The service must renew the lease every five
minutes (”I am still here”)
– When the lease expires the LUS deletes the
service object from its database
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Jini – dead service
Lookup
service
Service
Client
Service registers
a service object
Client queries LuS
LuS returns a lease
Service renews lease
LuS return service object
Service crashes
Client tries to call service
Client gets
RemoteException
Lease expires
LuS discards the
service object
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Client discards the
service object
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Middleware and Openness
In an open middleware-based distributed system, the protocols used
by each middleware layer should be the same, as well as the
interfaces they offer to applications.
Early Binding: Language, Interface.
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Overlay Network Based on MOC &
Socket
• Sockets gives a simple abstraction for
message transfer over network
• With sockets one can construct a new
abstract network over the underlying IP
network
• Prerequisites:
– New address schema (Naming) and its
– Name resolution mechanism (routing)
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Web naming scheme
• Uniform Resource Identifiers
(URI) come in two forms:
–URL: Uniform Resource Locator
–URN: Uniform Resource Name
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Uniform Resource Locators
Common schemes
Often-used structures for URLs.
a)
Using only a DNS name.
b)
Combining a DNS name with a port
number.
c)
combining an IP address with a port
number.
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Name
Used
for
Example
http
HTTP
http://www.cs.vu.nl:80/gl
obe
ftp
FTP
ftp://ftp.cs.vu.nl/pup/min
x/README
file
Local
file
file:/edu/book/work/chp/
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telnet
Remot
e login
telnet://flits.cs.vu.nl
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Uniform Resource Names
urn :
isbn
:
0-13-349945-6
• Three parts: Scheme : Name space identifier : Name of resource
• The name space identifier determines the syntactic rules for the third
part. The third part may have different structure depending on the
name space identifier. So URNs are not publicly resolveable.
• In contrast to URLs, URNs are location-independent which means
URNs usually are not related to any specific entity (only used as a
name space).
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Locating URL (Name Resolving)
• Domain Name System
(HostName -> IP)
– Each computer has to be
assigned an IP address and DNS
server IP address manually or
through DHCP server.
– DNS Request (nslookup) sends
the hostname to the specified
DNS server.
– The DNS server returns the IP if
it knows it, otherwise, the request
is forwarded to upper-layer DNS
server.
Record of
E’s IP
User host
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Data Representation / XML (1)
• Extensible Markup Language
(XML) is a standard format for
interchanging structured
documents.
•
•
•
<?xml version="1.0" ?>
XML is designed to describe data <note xmlns:note=“http://tv.com/note.xml”>
<note:to>Tove</note:to>
HTML was designed to present
<note:from>Jani</note:from>
data.
<note:heading>Reminder</note:heading>
<note:body>Don't forget me this
Anyone can use XML to define
weekend!</note:body>
data in any tree-based structure.
</note>
• To be able to distinguish different
structures, XML Name Spaces
are used to enable different
structures of data to co-exist in
one document.
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Data Representation /XML (2)
• It is the reader application’s responsibility to understand
(parse) the elements in the XML document.
• Extensible Stylesheet Language Transformations
(XSLT) is a language for converting XML document from
one structure to another.
• XSLT is one way to help the interoperation between
distributed systems using different standards.
Input
XML
XSLT processor
Output
text
XSL transformation
rules
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Data Representation /XML (3)
•
•
•
•
XML is self-describing
XML treats all data as text
Significant memory overhead
Examples:
–XML-RPC
–JXTA messages
–Web Service, SOAP
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Overlay Networks
• Examples:
– P2P networks (Content-oriented network/P2P
file sharing, SIP)
– Naming: auto-generate UUID and register
– Routing: JXTA Rendezvous etc
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Web Services
XML Web services are the fundamental
building blocks in the move to distributed
computing on the Internet, it takes the ideas
and principles of the Web and apply them to
enable computer-computer interactions (Bto-B transactions):
•
•
•
•
SOAP
SOAP (Simple Object Access Protocol):
provides a simple and lightweight
mechanism for exchanging structured and
typed information using XML:
WSDL (Web Services Description
Language): describing service information
including message contents, service location,
communications protocol (IDL).
UDDI (Universal Discovery Description and
Integration): for registering Web services so
that potential users can find them easily
(service yellow pages/directory service).
programming-language neutral
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Clients/Servers Architecture
• General interaction between a client and a server.
1.25
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Three-tiered C/S model
•
The general organization of an Internet
search engine into three different layers
1-28
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Multitiered Architectures
• Alternative client-server organizations (a) – (e).
1-29
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Conclusion
• Distributed System technologies:
–
–
–
–
–
Procedure- and object-based communication
MOM and socket
Naming and resolution
Overlay networks
XML, Software architecture
• Today
–
–
–
–
Service-Oriented Architecture (cloud computing)
Dynamic service access (late binding)
Open standards
Still ’standards wars’: e.g. HTML5 video, Android
versions
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Perspectives on interactive
systems
Contents
• Interactive systems from a user
perspective
• Interactive systems from a systems
perspective
• Desirable properties of tools
• Analysis of Java, Python, C#
• Other considerations
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Interactive systems from a user perspective
•Supports cooperation between, and in, groups of users
•CSCW, Wiki, Facebook, Twitter, Second Life, Blue Mars
•Interactive spaces
•Supports shifting modalities and forms of interaction
•WWW
•Cell phones, PDA
•Voice, gesture and tactile interfaces (wii, iPhone)
Interactive systems from a user perspective
•Supports mobility and distance
•Users moving in the real world
•Users moving between different systems
•Supports interaction with resources in the environment
•File sharing (transparent document management)
•Useful devices, sensors
Interactive systems from a systems perspective
•Distributed systems
•Hierarchy: Client-Server, Peer-to-peer, open/closed
•Computer communication issues
•Transport, interaction protocols, security
•Heterogenous systems and general interoperability
•Hardware
•Operating systems
•Programmering languages
•Software versions
Interactive systems from a systems perspective
•Exotic hardware
•Cell phones, sensors, RFID, micronets
•Dynamics
•The availability of resources; users, clients, services
•Establishing and maintaining interaction sessions
To build interactive systems tools
are needed
• Communication methods and protocols
• Programming languages
• Runtime environments
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Desirable properties of tools
Hardware independence
OS independence
•Cell phones
•PDA:s
•Wearable computers (laptops)
•Server computers
•Linux/Unix/OS X
•Symbian/Android
•Windows family
Computer communication
•Remote Procedure Call (RPC)
•TCP/IP, Serial ports, USB, FW
Desirable properties of tools
Hardware independence
OS independence
•Cell phones
•PDA:s
•Wearable computers (laptops)
•Server computers
•Linux/Unix/OS X
•Symbian/Android
•Windows family
Computer communication
•Remote Procedure Call (RPC)
•TCP/IP, Serial ports, USB, FW
Virtualization
Desirable properties of tools
Hardware independence
OS independence
•Cell phones
•PDA:s
•Wearable computers (laptops)
•Server computers
•Linux/Unix/OS X
•Symbian/Android
•Windows family
Computer communication
•Remote Procedure Call (RPC)
•TCP/IP, Serial ports, USB, FW
Virtualization
Host system:
vmWare, C++..
Language system:
Java, Python, elisp
Analysis of Java, Python, C#
Java
Python
C#
Hardware independence
yes
yes
yes
OS independence
yes
yes
no*
Computer communication
yes
yes*
yes
Security
yes
no
yes*
Analysis of Java, Python, C#
Java
Python
C#
Hardware independence
yes
yes
yes
OS independence
yes
yes
no*
Computer communication
yes
yes*
yes
Security
yes
no
yes*
To reflect upon …
• interaction implies communication
• choose tools that enable and simplify
communication (e.g. C# i Windows)
• make abstract communication (t ex XML-RPC,
SIP, SOAP)
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• Other considerations:
– asyncronous communication
– object-oriented programming
– mobile code
– the agent metaphor
– launch and maintenance
• code distribution
• version management
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End
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