Internet devices and services - summary

Memory

One primary theme of this unit has been about what one can do to get internet devices and services with restricted memory

Programming on limited devices

• Assembler-level
• C
• Small Java virtual machines
  • CLDC with KVM
  • Limited display MIDP
  Will be examined

Multi-language programming

• C/Assembler interface
• Java/C interface - JNI
• C#/VB/Eiffel/Python/... (not covered)

Standardised devices

• HAVi for home-audio visual devices
• CEBus for general home devices
• Toys API?

Service definitions

• Java interfaces
• WSDL descriptions
• Web service implementations :-(
• Many others exist: CORBA IDL, RPC IDL

Internet services

• Combination of advert/lookup/invoke
• Many issues in advert
  • lifetime of advert
  • unicast or multicast
  • advert: service plus additional information
• Many issues in lookup
  • pattern/object matching
  • unicast or multicast
• Many issues in invocation
  • remote reference (late binding?)
  • remote stub (early binding?)
  • mobile object (remote becomes local)

Programming models

• Remote method/procedure call using remote references
  • RMI proxy object
  • Web service URL
• Mobile objects
  • Code mobility
  • Remote class definitions
• Hiding protocols: half objects
• Event queues of remote listeners
• Message systems

Jini

• Java-specific internet service middleware
• Good API
• Lousy environment
• Allows choices of early/late binding, remote references/mobile objects
• Addresses issues of network fragility

Web services

• Multi-language service middleware
• Lousy API
• Very good to poor environments
• Uses late binding RPC model only

Future directions

• More physical objects will contain microprocessors
• Many of these will have some sort of network connection
• The devices will have a vast range of computational capacities, from "dumb" to PC equivalent
• Most will run "industry standard" languages such as C, Java, VB.Net (?), C# (?)
• The devices will have a large variety of I/O mechanisms, such as stripped-down GUI and others: temperature sensors, intrusion detectors, keypads, etc
• They will run a variety of advert/discovery protocols: SLP, Jini, Web services, ...
• The scale will vary from large identifiable services such as Passport to small devices you aren't really aware of
• Downer: in order to succeed, internet services must become invisible - your resume says "I built something that everyone uses, but no-one knows about"