Formal Foundations for the Evolution of Hypermedia Systems

Mª José Rodríguez-Fórtiz (Universidad de Granada)Lina García-Cabrera (Universidad de Jaén)José Parets-Llorca (Universidad de Granada)

Why Evolutionary Hypermedia?

Dynamic and evolving nature of Hp Systems. Represents a conceptual domain Ways of representing, structuring and browsing it.

Life-cycle- of Hp is not sufficiently considered. Implicit, diluted and unaffordable structuring

process inside the documents.

A Semantic-Dynamic Model based on SystemsMemorisation

system:information semantics, conceptual domain.

Navigation system: extends semantics, order relationships to

cover the conceptual domain.

Evolution

Changes and updates integrated in the

development process

Formalisms of a Higher Abstraction Level

Meta-levelEvolution operations (Ace)

(meta-operations with preconditions or meta-restrictions)

Memorisation System

MS = (CS, RT)

concepts, items, associations,

restrictions

Navigation SystemNS = (CSn , RTn, PN)

navigation rules or restrictions

changes changes

Formalisms of a Higher Abstraction Level

Meta-levelEvolution operations (Ace)

(meta-operations with preconditions or meta-restrictions)

Memorisation System

MS = (CS, RT)

concepts, items, associations,

restrictions

Navigation SystemNS = (CSn , RTn, PN)

navigation rules or restrictions

changes changes

Memorisation SystemSpecification: Conceptual Structure CS

concept, C

item, II

association

concept-item, Ai

association

concepts, Ac

Solar System

Stars Planets

Venus Earth Sun

Countries Moon

Portugal

Oceans

P1

part_of

is_a

part_ofpart_of

part_of

is_a is_a is_a

rotate rotate

rotate

def

def

list

list photos

photos

nova

supernova

map

history

chemical composition

S2

Su2

Su1

S1

S3

M1

O1

C1

Po2

Po1

C2

cities

E1

map

part_of

(Graph)

(Temporal logic)

RTs : “is_a association is not recursive”<c, is_a, c1> not <c1, is_a, c> c, c1 C

RTa: “every planet will rotate around the sun”<c, rotate, Sun> <c, is_a, Planets> c C

Memorisation SystemSpecification: Restrictions RTs & RTa

Formalisms of a Higher Abstraction Level

Meta-levelEvolution operations (Ace)

(meta-operations with preconditions or meta-restrictions)

Memorisation System

MS = (CS, RT)

concepts, items, associations,

restrictions

Navigation SystemNS = (CSn , RTn, PN)

navigation rules or restrictions

changes changes

Ace:add_concept_assoc:

<Saturn, is_a, Planets >Meta-RT: (set-theory)< Planets, is_a, Saturn > Ac

(temporal logic)<c, is_a, c1> not <c1, is_a, c>

with c = Saturn and c1= Planets

Ace:add_concept: SaturnMeta-RT: Saturn C

Evolving MS: CS CS'

CS' = (C', II', Ac', Ai') C'= C {Saturn}; II' = II ; Ac'= Ac {<Planets, is_a, Saturn>}; Ai'

= Ai

Memorisation SystemEvolution: Modification of CS

Internal propagation of the changes

(Set-theory) (Set-theory or Temporal logic)

Memorisation SystemEvolution: Modification of RTa

(Predicate temporal logic)Ace: addRest (<c,is_a,Planets> <c,rotate,Sun>)

Meta-RT: “cycles in concept associations are not allowed” addRest(ac2, ac1) not isRest(ac1,ac2) ac1,ac2 Ac

This clause can be instantiated:addRest (<c, rotate, Sun>, <c, is_a, Planets>) not isRest(<c, is_a, Planets>, <c,rotate, Sun>)

(Temporal logic)

RTs : “is_a association is not recursive”<c, is_a, c1> not <c1, is_a, c> c, c1 C

RTa: “every planet will rotate around the sun”<c, rotate, Sun> <c, is_a, Planets> c C

Memorisation SystemSpecification: Restrictions RTs & RTa

Formalisms of a Higher Abstraction Level

Meta-levelEvolution operations (Ace)

(meta-operations with preconditions or meta-restrictions)

Memorisation System

MS = (CS, RT)

concepts, items, associations,

restrictions

Navigation SystemNS = (CSn , RTn, PN)

navigation rules or restrictions

changes changes

Navigation System:Specification: SubGraph CSn

Navigation System:Specification: Restrictions RTn

(Temporal logic)

RTn:

c.Portugal.map c.Countries.list and a.is_a

c.Portugal.map c.Countries.cities and a.is_a

c.Portugal.history c.Countries.cities and a.is_a

Navigation System:Specification: Creating PN from RTn

(Petri Nets)

Formalisms of a Higher Abstraction Level

Meta-levelEvolution operations (Ace)

(meta-operations with preconditions or meta-restrictions)

Memorisation System

MS = (CS, RT)

concepts, items, associations,

restrictions

Navigation SystemNS = (CSn , RTn, PN)

navigation rules or restrictions

changes changes

Navigation System: Evolution: Modification of RTn

(Predicate temporal logic)

Ace: delRest ( c.Portugal.map c.Countries.list and a.is_of )

Meta-RT: “Every item must be reachable”

delRest(c.i, nav_rest) existRest(c.i, nav_rest1) or ( existRest(c1.i1, nav_rest2) and ref(nav_rest2, c.i) ) c C , i II,

Navigation System: Evolution: Generating a new PN

Earth.map

Sun.chem_comp

Countries.list Countries.cities Sun.photos

is_a

rotate part_of

Portugal.history Portugal.map

Oceans.list

is_a

part_of

Evolution and flexibility

InformationSystem

CSm1

.

.

.

CSmn

CSn11...

CSn1n

CSnn1...

CSnnn

PN1n1...PN1nn

PN111...PN11n

PNnn1...PNnnn

PNn11...PNn1nDifferent ways of representing,

structuring and browsing the same Information System

Specification formalisation

Memorisation System Graphs Temporal LogicConcept (C ) Labelled node Proposition

Item (II) Labelled leaf node PropositionRelationship between concepts (Ac)

or concepts and items (Ai)Labelled arc Formula with temporal and

logic operatorsNavigation System Petri Nets Temporal Logic

Concept or item Place PropositionOrder relationship between con-

cepts or itemsTransition and arcs Formula with temporal op-

eratorDependence relationship betweenconcepts or concepts and items

Transition and arcs Formula with logic operator

Navigation Firing transitions Instantiation of formulas

Evolution formalisationMemorisation System Graph Theory Predicate Temporal

LogicOperation Set operation Predicate

Meta-restriction Reachability function Temporal formulaModified aspect Set Variable

Navigation System Predicate TemporalLogic

Operation PredicateMeta-restriction FormulaModified aspect Instantiation in the

variable of a predicate

1) Consistency

2) Propagation inside

3) Propagation outside

Evolving Actions

5) CS evolves (Set Theory)6) RTa evolve (PTL)7) If RTa change --> CS changes8) RTn evolve (PTL)

1) RTs or RTa <--> CS2) CSn, subset of the CS If CS changes --> CSn changes3) RTn constraint CSn

4) PN created from RTn. If RTn change --> PN changes

Conclusions MS and NS allow a specification and management of

the semantics of information and its navigation in a separated way, using different formalisms.

The model guarantees the conservation of the integrity of the system by meta-restrictions. Evolution actions inside and outside each system.

The selected formalisms allow an easy specification and change of the structure of each system.

These evolution formalisms can also be applied to other evolving systems (reactive or temporal ones).

Suggestions for discussion topics

Evolution during the development process.Specification and evolution: relationships.Evolution (changes in the structure):

Meta-level.Guarantee of consistency: invariants, pre or

postconditions.Change impact, propagation of the change.

Which formalism is the better?