1. Self-updating Software Barbara Liskov & Daniel Jackson Progress Report, June 1999
write on board in advance: handouts, names, Hoare quote
do first 6 slides quickly
remember to leave time for students to fill in info sheet: 5m?
don't dwell on first abstraction slide
might not have time for last two abstraction slides

2. overview motivation pervasive computing
personal devices, appliances, sensors & actuators
dynamic reconfiguration
change in needs, location, resources
fixing errors and upgrading function
challenges
safety & reliability
updates are consistent & reversible
automation
minimal user effort
performance
no service interruption
scales to large distributed systems
multiple component suppliers
1/16/2019
© Daniel Jackson, 1999

3. progress: dependency model
server
dependency model
decouples components from one another
components chosen by specifications
makes automated repair & update possible
runtime scheme
user requests new functionality
eg, component A needs S
client machine looks in local DB
if not found, requests spec from server
server identifies provider (eg, by URL)
client downloads & integrates component B S
provider B
client A B
1/16/2019
© Daniel Jackson, 1999

4. progress: object update
context
in context of Thor, an OODB
huge state, widely distributed
trillions of objects
millions of clients
update should be atomic
lazy update scheme
update treated as a transaction
object only updated when necessary
global state may be inconsistent
but user transactions never notice
site 1
site 3
site 2
circles are individual objects
arrows are object refs
green newer than red
1/16/2019
© Daniel Jackson, 1999

5. plans (next 6 months) dependency model finish design
build initial infrastructure
demonstrate on
Java packages
small shareware programs
object update
refine design
build scheme for lazy updates
good performance
clean & desirable semantics
Thor persistent object store
1/16/2019
© Daniel Jackson, 1999