Adding Multimedia Collections to the Dexter Model - CiteSeerX

Adding

Multimedia

Collections

Franca Garzotto,

Luca Mainetti,

to the Dexter Model Paolo Paolini

Politecnico di Milano - Department of Electronics and Information Piazza Leonardo & Vinci 32-20129 Milano - Italy Phone: +39-2-2399.3623 Fax: +39-2-2399.341 e-mail: {garzotto, mainetti, paolini]@elet.polimi.it

1

ABSTRACT] The

Dexter

Model

defines

the

notion

of

INTRODUCTION

The Dexter

atomic

1

AND

Model

[19]

defines

a set of primitives

components and composite components, but it does not prescribe, nor it suggests, any particular structure for composite components.

structure of nodes and links. The runtime layer describes the mechanisms to support the interaction of the user with

upon three layers.

This paper proposes a specific type

of composite component, called “collection”. A collection is a container holding several members. Collections can contain other collections (nested Collections

can be regarded

by exploiting

as sets, but they

collection, related

links, etc.

collections

allow the design

Concepts proposed

their structure, their number of possible

contribution independent

examines

the interplay

collection

navigation,

for

collections,

between possible

as well

standard

as the

and a It also

navigation

synchronization

for

the data

to the storage layer,

of collection-navigation as extensions

and the

and collection-

to the runtime

layer.

consists in pulling together several proposals, sometimes extending and them. In addition, we discuss a number of

authoring mechanisms for collections, we propose a more relevant role of collections within the navigation paradigm,

the

definition of a mntime support (which could be used to extend the runtime layer of the Dexter Model).

and an interpretation of the behaviour of collections takes into consideration also active media.

KEYWORDS:

In Memex,

Dexter

Design, Collection,

Model,

Composite,

Hypermcxlia

Vannevar

Bush proposed the idea of trail

group of elements gathered from a mass of information

Guided Tour, Active Media

bound together to forma

1Permission

to copy without

fee all or part of this material

is

[3], a and

new “book2.

2 “...when numerous items have been thus joined together to form

arKVW specific permission. 43 1994 ACM 0-89791 -640-9/94/0009/$3.50

’94 Proceedings

that

[24], used to TEXTNET implemented trails as paths generate multiple different linear documents from a single hypertext network, and [15] exploited the notion of trail as “guided tours”, to support navigation of naive users across educational material.

granted provided that the copies are not made or distributed for commercial advautage, the ACM copyright notice and the d-t title of the publication and its date appear, and notice is given that copyright is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee

ECHT

A

of the generic by the Dexter

similar to what we call collection have been several times, by several authors. Our

generalizing

and

strategies

requirements

describes

collection can be considered a specialization notion of composite component introduced Model for the storage layer.

and implementation of complex synchronisation strategies, difficult to obtain otherwise. The paper describes the motivations for using collections, navigational capabilities authoring mechanisms.

is based

storage layer

as an extension

notions

synchronization,

Collections introduce a navigational pattern, based on their structure, that is different from the standard node&link navigation. If active media are considered,

The

The model

the application. The within-component layer describes the internal structure of elementary values (e.g. a text, an image, a video, etc.). This paper proposes the adoption of the notion of

can also have an inner structure. Collections can be created in several ways: manually, through queries, by operations on other collections,

applications.

for

describing

collections).

hypermedia

BACKGROUND

a trail, they can be reviewed

70

in turn, rapidly

or slowly...”

[3]

September

1994

way of aggregating related objects. Query (i.e., search) is performed over some type of collection...”.

The notion of guided tour is investigated in fiMher detail in Trigg’s paper [25]. Trigg clearly highlights the role of guided tours in hypertext the intelligibility

applications,

of hypertext

as a way “to ensure

documents

especially

occasions when the authors are not present”. holds together

a number

of Tabletops,

together to form an arbitrary a device of Notecards

In our work

on

connecting

them

logical

primitives

useful

of hypermedia

for the

applications

[4,

6,7,8,9, 10], we have defined several types of composite among them, the most important are node, en[ity, web and

graph structure. A Tabletop is

for displaying

to define

design and implementation

A guided tour

collection. Informally speaking, a node is the basic unit of navigation and it corresponds to what is typically intended as such in the hypertext field, or to a card, in card-oriented systems. An entity is a composite, grouping all the nodes

several values in a

single co-ordinated screen layout. The user interaction with a guided tour exploits the topological arrangement of tabletops in it, through commands as Start, Next, Previous, Jump. The user can also leave a guided tour, following the links outgoing from the cards in a Tabletop.

corresponding

Marshall

the nodes corresponding to the monument “Duomo”). web is a composite, that generalizes the notion of link.

analyzing

[20] further

explores the notion

presentation

conventions

of guided tours,

and issues related

the design of expressive and intelligible

collection

to

can h

traversed

commands

such as next,

previous,

ways

and

in

collections;

mechanisms

members

as general as possible, we

for

section

creating

3

we

collections;

describe in

several

section

4 we

examine the navigation capabilities determined by collections; in section 5 we examine the usage of active

automatic

by the user through etc.)

together

of node, providing a short explanation for it, and of link, relying upon an intuitive understanding of it. In section 2 we present an informal introduction to nodes

Zellweger also model, specifying

in three

grouping

media

and by direct

with

collections;

conclusions,

choice of the item of interest. A major contribution of this work is the notion of active path entries, i.e., entries that have their own behaviour, and the notion of Scripted

collection directions

comparing

in

section

more

6

precisely

with previous works, of our research.

we

draw

the

our

notion

of

and illustrating

the future

Document, which is “a procedural programmable path with active entries, called scripf”, Multimedia entries are presented as a special case of active entries.

2

Parunak’s work [26] points out the relevance of set oriented

We need to introduce

hypertext.

is a value, i.e. an atomic piece of information,

which,

context

be

Parunak’s

main

objective

is

to

A A

will not use the notions of entities and of webs (which are not crucial to explain collections). We will use the notions

the traditional navigation paradigm, and convincingly argues that path constructs should become frost-class citizens in hypermedia systems. Two relevant issues are raised: the structuring of paths (linear, branching,

that a path

a composite

In order to keep our discussion

Zellweger [29], within the context of her proposal of Scripted Documents, introduces paths as a way to augment

control, one step at the time (controlled

is

world object” (e.g., all

(either nodes or webs or entities or other collections). The notion of collection is the central focus of this paper.

guided tours.

conditional) and their granularity. introduces the elements for a runtime

to the same “external

INFORMAL

PRESENTATION

OF NODES

AND

COLLECTIONS

support

taxonomic reasoning, i.e., the task (common to many applications domains) of dealing with the comparison and classification of pieces of information. A model based on set theory and set operations, Parunak observes, is more

of

a

decomposed.

given

the preliminary application,

A slot is strictly

Dexter Model calls “atomic component

notion of slot. A slot cannot

correspondent

in a

further

to what the

component”3,

that is to say a

elementary

both by the user

that is considered

appropriate for this task than a graph based model. He presents a system that supports creation and manipulation

and by the application. A slot may have a complex inner a stmctute, but (as it is the case for atomic components of

of sets , and navigation

the Dexter model) there is no possibility across this inner structure.

operation

is “not moving

based hypermedia,

across them. The basic browsing from node to node as a graph-

but moving

from an artefact to one of

A node is a composite,

the sets in which he is member, and then to other members

slots, and represents

of navigation

which groups together a number of a logical

unit

of information

(and

of that set”. Parunak observes that it is desirable to provide both set based and graph based navigation

in a hypermedia

9 We do realize

system, but he does not discuss the issues raised by such a hybrid approach any further. Collection is a term also used in the context of Object Oriented Data Bases. In [28], a collection is considered “a

ECHT

’94 Proceedings

that the authors

of the Dexter

Model

have a

dtiferent opinion, since they declare that “atomic components are what is typically thought as nodes in a hypertext system...” [19]. This opinion however, seems to be in contradiction with what it is said elsewhere in the same paper. In fact a node, intended as a navigational unit, holds, in general, several atomic components together.

71

September

1994

navigation) monument

for the user. Examples “Duomo”,

example

of nodes could be the

the shop “Armani”,

Collections

de Milan”. The slots belonging to the same node are closely related each other and they concur the description is a composite,

including

several nodes. There

are several different reasons to put a node in a collection. One reason could be the need of partitioning the set of nodes in semantically consistent groups (taxonomy) [23]. Collectionss “Historical

such periods”,

as

“Artists

lives”,

of the notion of collections. Another reason to put a node in a collection need of organizing as “Erotic

Art”,

a specific presentation.

or “Figura

Serpentina”,

more

subjective

arbitrariness

points

can very from

of

The

such

Arbitnuy

presentation collections

likely

slots of the collection

collection miniature

etc. Other

node, instead, can be derived6

from

for example, in the

nodes As far as inner structure

to

culturrd perspectives,

is concerned,

a collection

can be

described in two ways: as a set of members

be

holding

together

the members in

a

topological arrangement. Typical structures used in applications are sequences (most common), trees (quite common), lattices and generic graphs (less common),

etc.

This is the reason why collections are so important for hypermedia application~ they allow a continuous modification and improvement of the way the content of an

etc.

Some operations

are easier to describe

collections

considered

collections, operations described

application is organizxxl and presented, without having to modify the core of the information (represented by the

Collections,

graphics,

node, beside the introductory text, there are the pictures and names of the paintings, members of

as a structure

nodes). This requirement [14], when he suggested

asscxiated

the collections; these pictures and these names are derived from the corresponding slots of the members.

nodes of

that, once they are defined, they are seldom modified. Presentation collections, instead, can continuously be modified, in order to make the content of the application more accessible, in order to accommodate new points of

premature

text, an introductory

the members of the collection. For the collection “Figura Serpentina”,

are usually quite stable, in the sense

view, in order to present different

directly

members). We consider this to a special node, that we call

an introductory

heterogeneous. Taxonomic

not to the as belonging

to

(i.e., containing

are

both nodes and other collections,

of

collections, in general are a mandatory requirement.

collections

(nested

Art”)

(i.e., containing

the same type), or heterogeneous,

collections

degree

(e.g. “Erotic

collection is very arbitrary, and based upon the subjective point of view of the designer of the collection itself.

of different types). Taxonomic homogeneous, bit this is not

other

collection node. Some of the slots of the collection node, contain new information: e.g. the name of the collection,

order to describe the manufacturing techniques. The choice of which paintings should be introduced in such a

can be homogeneous

may include

to it (i.e. information

extreme. Consider, for example, a collection such as “The making of Painting”, where some paintings are used in

Collections

also include

another collection. A collection may also have information

are an example of

view.

mild

by

We use the generic term member, to refer to an object included in a collection, both if it is a single node, or

use

this type of collections. Presentation collections are more arbitrary than taxonomic collections, since they correspond to

in the sense introduced

are seldom found, but they can’t be excluded.

could be the

Collections

may

collection

“Paintings”,

are an example of this taxonomic

structures,

collections). The collection “Monuments in Milan”, for example, may contain the collections “Romanesque Milan”, “Gothic Milan”, “Renaissance Milan”. These latter collections, in turn, may include other collections, in order to further organize the material. Mixed situations, where a

of an object 4. A collection

of virtual

Halasz.

the hotel “Hotel

are

difference of (the navigation if

the

inner

sets

union

of

two collections, etc.). operations) are more

structure

of

considered (e.g. Next, Previous, First, collection structured as a sequence).

was already stated by Hrdasz avoidance of the “problem of

and implement

(e.g.

the

if two

Other easily

collections

Last,

etc. for

is a

organization”,

by using virtual structures. in our interpretation, could be intended as an

3

AUTHORING

OF COLLECTIONS

1. 2.

operations are needed, in order to create a collection: definition of the set of members definition of the inner structure of the collection, and placement of the members into it

3.

definition

Three 4 As we have said in the previous external

objects, such as “Duomo”

smtion, to entities

we usually

associate

[4, 7] rather than to

nodes. An entity is a composite made of several nodes, cmnected by structural links. In this paper we wish to avoid the additional level of complexity introduced by entities, and therefore we assume that all entities (e.g., ‘DuOmo”) 5 The examples

application

ECHT

consist of a single node.

here indicated are “loosely” “Art-Gallery” of Microsoft.

’94 Proceedings

of the node associated to the collection

related to the

c Informally

speaking, a slot “s” is derived horn slots s1, 52.. sn if it can be defiied a function f such thats = f(s 1, S2...sn).

72

September

1994

3.1 Definition We

have

members

of the members

identified

six

basic

of a collection:

set-oriented,

of a collection

link-oriented

and

basic methods can be combined The built-in require

creation

another

to

the

pick-up,

session-based. method

The

These

point.

In

built-in

mechanisms

starting

point

in-line

is a collection

a collection with and

is very

the nature of a set of links

the set of nodes connected to the members of the original

this

collection.

the basis for any authoring

systems provide

method for creating

and it is very much

(possibly typed). Applying the links to all the members of the collection, we obtain another collection, consisting of

that does not

as a starting

respect it cart be considered

define

intentional,

together.

is the only

collection

activity. All the authoring

methods

built-in,

The link-oriented powerful, hypertext,

L&us

assume, for example,

that we have a link

“author” associating each painting to the corresponding painter. Let us assume that “Rcmm-1” is a collection of

to

paintings;

applying

the link

“author”

the collection “Room-l”.

with each node type. Untyped systems usually partition the global set of nodes into smaller collections, according to some user directives. In HYPERCARD, for example, stacks are built-in collections. Creating a card in a stack

We have been recently experimented quite extensively the link-oriented method of building collections [21]. The method seems to be quite interesting, since it couples

automatically TOOLBOOK

places it in that collection. play art analogous role.

The intentional

creation

selection mechanism.

of a collection

Books

to which

applied, and a selection criterion.

in

Most

systems

support

session-based

methods

to build

collections. The “history”, i.e. the set of nodes that a user has visited during a session, is a typical session-based

is based upon a

the selection

who have an exhibit

expressive power with relative easiness of usage.

in

collection.

It is necessary to specify a collection

(or a set of collections),

of all the painters

to it, we can obtain

create some collections. The systems that have typed nodes, for example, have a built-in collection associated

Some systems simply

must be

history,

A selection engine must

other

insert

systems

all the visited

allow

specialized

nodes in the histories

(e.g.

be used, in order to interpret the selection request and to compute the result. The result is the collection of all the objects satisfying the selection criterion.. Different mechanisms of selection can be provided e.g.

partitioning the visited nodes by type), or they may require an explicit marking of the nodes that should be inserted in the history. Some systems treat history as an ordinary collection; other

Data Base queries, keywords

systems allow special operations only on the history.

Intentional

creation

It is not applicable proper

attributes

search, content search7, etc.

of collections in all situation

(for

Data

is a very powerful

tool. In practice,

however. First of all the

Base queries)

and keywords

must be prepared in advance and intrusively

prcdefined,

method

is very

popular

among

method

is

typical

for

hypertext

building

In most applications

and can’t be modified

We are experimenting,

collections

are

by the reader. The most

instead

a different

where a second-k?vei author, mechanisms for creating new

can use collections,

environment a in

variety order

of to

provide specialised access paths for the final readers.

arbitrary

collections, when the intensional selection can’t be applied. The set-oriented method exploits the unstructured nature of collections, applying set operations, Intersection, Difference, etc.

all the six

but a few of them, with a

common tools provided are queries (intentional definition) or history; the collections created by the reader can be operated upon only in a special manner, and are kept distinct from the ordinary collections.

systems. The author manually selects the members of his/her interes~ while navigating around in the application. The pick-up

do not provide

collections,

number of restrictions.

embedded in

the description of the information objects, in order to allow queries. In addition, this technique requires a (relatively) skilled user, able to use a query language and to precisely select the objects of hisfier interest. The pick-up

most environments

methods for creating

3.2 Definition

of the inner structure

of a collection

such as Union, The method

to define

the inner

structure

of a collection

Let assume, for example, that we start with two collections in Area 1“ and corresponding to the “Monuments “Monuments in Area 2“; and also we have the collection

clearly depends on its topology. If the collection is organized as a sequence, it is required a

“Churches

in Milan”.

Through

the union of the f~st two

collections,

and the intersection

of the result with the third

achieved either manually, specification, i.e., through

collection, we can obtain a collection having all the churches in Areas 1 and 2 of Milan.

total ordering

among

For lrees and lattices, “tradhional”

text-retrieval,

or modem

image

The ordering

content

lattices

be specified. or other

a partial

Most

kinds

can be

or through an intensional the explicit definition of the

ordering criterion (in our applications, in general, allow both manual and intensional orderings).

as members

must 7 Either

its members.

of

we do

order among the members the

of generic

systems

allowing

trees,

graphs (e.g. Notccards),

search.

ECHT

’94 Proceedings

73

September

1994

make use of graphic interfaces

“Gothic

in order to allow the author

section),

to place the members in the proper relationships. 3.3 Definition

of the node associated

to the collection

Milan”

as a guided

tour

so that he can visualize

(discussed

in the next

the nodes one after the

other. We may want to add information

about how to get

from a monument

This information

to the next monument.

does not belong to the members of the collection, The node asswiated role~

to a collection

depends on the way (order)

plays three distinct

We

can consider

these

we arrange

traveling

tips

since it

the monuments. as slots

of the

2

it helps the reader to understand the content of the collection. It provides additionrd information for the collection.

collection node, which are to be presented interleaved with the members of the collection. The use of the collection node as a device to access the

3.

It provides

members of the collection

1.

mechanisms

to access the members of the

information

taken from the members

the members, where

the

part

new

of their

content,

information

4

it

may

happen

etc.). We call

is stored,

that

a collection

beside the one provided

Let us assume, for example,

NAVIGATION

AND

COLLECTIONS

(e.g., the names of own

We have identified

slots

slots

requires

two basic ways to navigate

collection: Index and Guided-Tour 2%189. In order to support index navigation, collection

and

derived slots, those where the information “borrowed” from the members is keptAs far as the second role for collection nodes is concerned, information,

is discussed at some extent in

the next section.

collections. In order to help the reader to understand the content of the collection, the collection node may present new information (e.g., a title, an introductory text, etc.) or

with links

a are

created between the collection node and each of the members (as well as their inverse one). From the collection node, using these collection

additional

links,

the user can select any

of the members; from a member the user cart return to the

in the introduction.

collection

that we let the reader use

node.

ElB!i!!?stith mlledion

Fig. 1- Collection

“Figura Serpentine”,

In order to support guided tour navigation,

showing collection

collection

provided

ECHT

at the same time.

’94 Proceedings

patterns that

he/she wants to use index or guided tour navigation. For index navigation, the user can select one of the members of

(see Fig.1).

and guided

links

we provide in our applications. Our collections are organized as sequences. The collection node shows all the members, with information sufficient for the user to identify them. The user can dynamically decide whether

to traverse the collection node. The collection node must be connected to at least one of the members (the “frost” item),

8 It is often the case that iodex links

members, and collection

As an example, let us describe the navigation

links

are created among the members, according to the topology of the collection. These collection links allow the user to move among the members of a collection, without having

in order to start the guided tour navigation

node, collection

ride)

tour links

are

randomly

If this is the case the reader

ean

navigation.

74

select

an item,

and start

fi-om there

a guided

September

tour

1994

the collection

and jump

back to the collection

to i~ from

node. With

there he/she can go

1), or a jump to “Monument”

guided tour navigation,

(up two levels), or a jump to

the next member of “Monument”

(Next at level -2).

from one of the members the user can use guided tour links (such as Next, Previous, First and Last), moving

around in

Monuments

the collection, without having to visit again the collection node. We also provide two ways to halt the guided tour

----

navigation from one of the members: going back to the collection node (Close command) or remaining on the current member, but outside the collection control (Stop

--

A Chumhes

command).

----

--

A Rom~esque Churches

Complex issues arise when a member of a collection is itself a collection (nested collections). Let us assume that collection Within

A contains

collection

A the collection

B as one of its members.

node “b”

is used to represent

B,

Fig. 2- Nested collection

From “b” it is possible to access the members of B, even if they are not directly Since

the

collections

members of A.

encapsulation

of

can be defined

collection

navigation

collections. When collections

can

This wide range of possibilities

collections

at several create

within

levels

a stack

other

of depth9, of

offers the advantage of an

efficient interaction for the user, if he/she wishes to change subject of the reading session; it has the disadvantage, however, of adding complexity to the interaction dialogue

activated

and to the lay out. are

activated

as

Indexes,

collections are used to implement hierarchical a master index allows to select sub-indexes,

nested The usage of collections

indexes, i.e. each one of

makes necessary to distinguish

standard link navigation navigation and collection navigation. The basic operation of standard link navigation is to follow two

them allowing to access a sub-index or an object, Nested collections used as guided tours are more complex

different

styles

of

a link from a source node and to “instantiate” (according to the Dexter Model terminology [14]) the target node, which means, in turns, to present the slots of the target node (or some of them, depending on the context of the link, as defined in [19]).

to manag~ most of the applications we have seen either do not allow nested guided tours, or, often, they show inconsistencies (if not mistakes) in providing a proper mntime support, thus becoming very disorienting for the user. Let us assume the we start a guided tour about the “Monuments of Milan” and within it we start a guided tour

Let us observe that the standard links attached to a node are relatively static: once they are defined they are seldom

on “Churches” and within it we start a guided tour about “Romanesque Churches”. The frost problem is to define

modified.

what is the proper behaviour

and they are subject to frequent

The links determined

when the end of the current

guided tour (Romanesque Churches)

place “Duomo”

is reached and a Next

“Churches”, described Gallery’?

time we

we provide

a new

other

applications

would

as not

executable,

in

of the consequences is that while standard links can be part

other

applications

situation;

(as

the

the

of the description

“Art

application. A more general problem concerns the possibility

links

include, for example, all the possible Next links, according to the different collections.

of directly

a level of nesting to another one (see Fig. 2). of “Romanesque Churches we could allow a next Romanesque Church (Next at current O), or a jump to “Churches” (up one level) or

a jump to the next member of “Churches”

of a node, collection

are instead

“external” to it. Answering to the question “what are the links outgoing from the node Duomo?”, we would never

would start again the guided tour on the current

jumping from From a node jump to the level, or level

collection,

operation

in our example);

the Next

in a different

are context dependent, changes. Every

different meaning for the notion of Next and Previous applied to it. Having in mind that a node can appear in several collections, and that collections can be also dynamically created during a session, this makes a substantial difference, with respect to standard links. One

operation is activated. Some applications would jump to the collection node of the next collection (say “Gothic churches”); other applications would jump back to the (i.e. collection node of the containing collection consider

by collections

or Previous

The interplay between standard links navigation and collection navigation is often the origin of confusing situations for the designer and for the reader.

(Next at level -

Let us assume that the user activates

collection

“A

(say

“Romanesque

Milan”)

it

“a”

(say

“S.Ambrogio”)

is selected. Is it possible to use the standard

and,

within

object

9 Say collection D, within C, within B, within A.

ECHT

’94 Proceedings

75

September

1994

(i.e., non-collection) links of “a”? If (following one of these links) object “b

yes, assume that (say S.Eustorgio),

implementation implementation

also belonging to “A, is reached. Which member of “A, object “a” or object “b”?

one is the current

engine,

Let

us

now

‘churches”)

assume

that

from

“A

operational

(say

specification

of

the

since

historical this

periods);

collection

but

node

this

has

is

never

(say

“Duomo”),

to

across

all

containing it, as one of their members. would not allow such a browsing. The above discussion

shows a crucial

the

space

prevents

us

to

elaborated, examples of confusing that most of the applications be simplistic,

discuss

the Dexter

collections

situations.

definition

Model

of the

takes

into

AND MULTIMEDIA

Model

must be provided,

synchronized

when active media

with a speech and a musical

the user can interactively the

We must say

the

The presentation in

of inconsistencies.

comment,

play with it, this has little

surrounding

synchronization multimedia slot.

more

we have seen seem either to

or to fall into a number

Dexter

(e.g. sound, animation, video, etc.) are considered. [1, 2, 19] have observed that some inner complexity of multimedia behaviour can be confined at slot (i.e. atomic component) level. If a slot, for example, contains a video,

of the links

other,

the

COLLECTIONS

upon of

for

It is already been discussed in [19] that some extensions to

created by the collections: they are active for the members if and only if the collection node has been activated before! Lack

layer

engine

based navigation.

also

Most applications

point

paper [11], we propose our runtime for collection

keen

it is possible, from art object “a”

browse

a ptvcise

applications.

5

issue is whether

of providing

consideration standard link navigation only; therefore we suggest an extension to it, in order to provide a better specification for collection navigation, which represents a great percentage of the dynamic behaviottr of many

activated by the user. Another

capable

for every possible user request. In

In this respect we believe that the current run-time

collection node”? If yes, what should be the meaning? One possibility is to go back to the collection node of “A (“churches”); this is confusing because the current objec~ “b, does not belong to that collection. Artother possibility is to go to a collection node where “b belongs (i.e. the confusing,

machine,

specification

a forthcoming

is reached, and from

there (following a standard link), node “b (say the Historical Period” 13th Century”) is reached. Is it pxsible from “b to activate the command “g&back-to-the-

collection

we

computational

collection

node “a” (say “Duotno”)

of applications, and for the design and of hypermedia systems. By runtime mean an abstract but unambiguous

environment.

Let

interactive

us

and

impact

slot

call

presentation

of

of a standard (i.e., not a collection)

a multimedia

environment,

requires

a

node,

synchronization

Simplistic applications are of two kinds: collection oriented or link oriented. Typical collection oriented applications are those where hierarchies of indexes are used to locate the node of

specifications: how the node should be started, how the respective playing of the different slots should proceed, etc.

interes~

Assuming

and no proper

standard

link

is defined

[1, 2,5,

for the

nodes. Typical

link

oriented

applications

are

those

where

a

support both for collection

and link

exhibit an inconsistent behaviour differently in conceptually similar leads

the reader

to confusion

navigation,

Milan,

very often

to the

“getting

If

ECHT

the

An interactive

video

suspended,

can be used as a guideline

’94 Proceedings

node

of

include10 , beside text and data, a speech commen~

comment.

is being

together control

started,

the

activated

with

the node spoken

for the video is provided. node

the

spoken

audio

comment

associated

is

to

the

must

be solved at its root a clean consistent run-time semantics for collection navigation and its interplay with standard link navigation is needed. Such a clean semantics can be provided by the precise definition of an abstract mntime which

and

synchronization

active slots are presented,

lost” syndrome. Our point of view on the subject is that the problem

slot

have been solved, we wish to address the

a node musical comment, a video clip with its own spoken comment, a number of slides, each one with a specific spoken comment. Let us also assume that the standard behaviour is the following: when the node is presented (or instanciatcd, in the Dexter Model terminology) the not-

(that is, they react situations), and this and

23] provide possible models

issue of collection synchronization. Let us assume that the nodes defined for the monuments

the only collection operation that is allowed is to go back @ the root of the the “home node”, which is typically taxonomic set of collections. More ambitious applications, that try to provide strong

engine,

that

synchronization

taxonomic set of collections is used to start the session, and from there on, standard links only can lx used to navigate;

quickly

12, 16, 17, 18, 19,22,

for this task, that we call node synchronization.

10The description enhancement development,

both for the

76

that follows

is a simplified

version

of the

of our “HyperMilano” application, currently under through a co-operation of Politecnico with some

reserchem

of the Institute

University

of Milan.

for the History

of Art at the Catholic

September

1994

video itself. The slides can be activated either manually in an automatic comment,

slide

associated

show:

in both

to each slide,

or

Let us assume, now, that we want to present the collection in the following

cases the spoken

way

for the collection,

supersedes the node

an graphic

a number

comment. For layout limitations, all the other information, except a few data, are not visible while video is presented;

spoken comment for the collection for the collection.

same thing applies for the presentation of the slides. The musical comment of the node is played in a continuous

Each

manner

(with

an automatic

the user interaction

restart),

independently

deal with the multimedia

of “Churches”.

values in the collection

One simple solution could multimedia slot, at collection

be to not node level:

from

the

video

a

and a musical comment (but

not

the

sound)

window, in order to select the node of his/her interest. The collection node has the following slots: title (own),

How to

background

node?

(own),

spoken

comment

(own),

musical

comment (own), video for each monument (derived). The most relevant aspect is that the collection node applies to

include any in the index

mode, the user can select the node of his/her

presents

with a title

size) windows,

associated with each monument while the collection spoken comment and the collection musical comment are being played in parallel. The user can “click” over a

with the node.

Let us consider now the collection

window

background,

of (small

the

interest and

video

slots

of

the

nodes

its

own

presentation

interact with it. In the guided tour mode, each node will be selected manually, through collection navigation. This

synchronization (i.e. small size and video only), which supersedes the presentation normally applied by the nodes

approach, as [19] has already observed, is simple, but of limited applicability, since it keeps out active media fmm

to those slots.

collections. Most approaches.

applications

require

more sophisticated

Glkcholl 3Iiue ..1 ,,

3

S%J.itj;’ “’ ....

+ti

---------

-,

*’

i

4-

..-

1 . . --

No&

m

TbXl

“

I

‘- ‘-

‘.,’,.

video1

Nods “~. ●.bo ~.—— Video M

‘,’, ,.,---

‘,,’ ,,

‘.’ .-. ( t’

Lik@=%”;

I

II

w-

4

. 0 I

o

Fig. 3-

Collection

“Churches”.

Synchronisation

Some collection

ECHT

’94 Proceedings

aspects

are graphically

described

by synchronisation

arcs.

links are omitted (see Fig. 1)

77

September 1994

Let us now define a different collection of “Churches”. introductory page, showing

collection

navigation,

node for the same

The

presenti,

the

“resume”

node

command

can

will

be explored

start playing

by

the

useq

the overview

state”, a “safe” state, or others?

6

The main difference,

(derived)

In this paper we have presented the notion of collection,

video

the other,

(see Fig. 3).

with respect to the previous example,

Suspending presentation

with

an additional

interactive

as

a specialized interpretation of the composite component of the Dexter Model. Our opinion is that the generic notion of composite in the Dexter Model should be refined in a number of “typical” possible structures, with the specification of their own navigation and synchronization features. Navigation and synchronization should be explicitly

taken into consideration

(i.e., supported)

in the

runtime layer.

lays in the presentation strategy. The video slots corresponding to the members, are played in sequence, one after

CONCLUSIONS

a

again. According to our model, the collection node has the following slots: collection title (own), background (own), introductory text (own), collection data (own), collection spoken comment (own), collection musical comment (own), video for each monument

section.

outlined by other of the state of a node

multimedia slots? Possible answers are “exactly the state reached at the time when the node was left”, “the initial

a musical comment complete the presentation. The overview video actually consists of “sukwequences” of the videos associated to each monumen~ memker of the If the playing is suspended, the node of the corresponding to the current video fragment is

problem,

(either standard node or collection node) when it is left for navigation what should be the proper presentation state of

and a text. When the user requests it, an overview video is started. The presentation, for the user, looks like an interactive video, with the usual commands. A spoken and

collection. monument

that has been discussed in the previous

additional

already researchers [17, 18], is the definition

We would like to have an over a background, a few data

Our specific main point is that collections are fundamental in many applications, therefore they should be explicitly

control.

acknowledged

the playing at a given frame, causes the of the member node, from which that frame

Our

second

as one of the typical point

is that

composite

collections

create

structures. new

links

was derived.

among nodes, not well represented

Let us consider, as a final example, the case where someone brings in a new video, showing an interesting walking tour in Milan. How can we include it in our

the Dexter Model. The third point is that the rnntime layer of the Dexter Model should also include a precise definition of the semantics for collection navigation, and its interplay with link navigation. The fourth point is that

application, and connect it to the previous material? This is the way we would proceed. We would select all the nodes that we consider related to the new video, inserting

coupling

pwerful

one being a short fragment, related to one or more nodes of the new collection. The collection node will consist of a background, a title, an introductory text, and the video fragments, all the slots being not derived. Each one of the slots will

have a “collection

nodes, members of the collection. Tour-l”

is activatedll

link”

multimedia

extensions,

interactive

control

and well-defined

consistent

Our interpretation of the roles of collections within applications, is exactly what was envisioned by V. Bush: to provide trails across large applications.

“W-

Trigg’s guided tours [25] can be viewed as a special case of

, the user can read the introductory

text, and possibly start the video, interacting

the

semantics. We are now in the position to make more precise bridges between our approach and the work of other researchers.

to the related

When the collection

with

already proposed by other authors, will allow to define and implemented sophisticated hypermedia applications, with a

them in a new collection, say “W-Tour-1”. The new video would be logically fragmented in a number of slots, each

video

collections

by the storage layer of

our collections.

with it in the

The main differences

lay in the fact that we

usual manner. Suspending the video, the user can visit the related nodes, and possibly their links to other nodes;

explicitly define the collection node (with additional information associated to it), we define a variety of

resuming the collection would start again the video. In this way, the new video has been fully integrated in the pre-

authoring mechanisms, we have analyzed the interplay between standard link navigation and collection navigation, we include extensions to active media, and, finally, we clarifying the notion of context dependent links (i.e. collection links).

existing

application,

but only minor The

with

changes

complexity

of

a certain

to the previous

the

number

interplay

synchronization with node synchronization, the interplay among standard navigation

11Possibly as a member of a collection 12This collection

ECHT

example

shows

links differently

’94 Proceedings

again

of additions,

definitions12.

0}

,

collection

Zellweger’s scripted documents have motivations very close to our collections; the main difference is that we

is analogous to and collection

provide structural primitives, trying to identify predefine patterns of behaviour. Zellweger, instead, leaves the role of defining the behaviour to scripts, which have the power

of eolleetions,

the advantage

of dealing

and the arbitrariness

with

of general programs.

from standard links.

78

September

1994

K. Gr$nbaek

and R. Trigg,

in [13],

advocate the use of

[4]

composite in hypermedia application their proposal, however does not precisely specify navigation (or synchronization) features associated to these composites; nor the application roles for such composite, with the

[51

works

on

active

media

synchronization

F., Paolini P., Totaro D. “HIFT Hypertext Interface for Information Systems”. In IEEE Sojhvare, Nov. 1993 De Mey V., Gibbs S., “A Multimedia Component Kit”, In Proc. 1993

exception of “link browser”. Previous

Cavallaro U., Garzotto

by

[a

for

be taken as a basis, and adapted to provide the primitives for collection synchronization that satisfy the requirements

Proceedings [7]

in Data an inner of the

[8]

constraint of homogeneity a variety of creation mechanisms. What we borrow from the Data Base approach is the idea that queries operate within mechanism

collections

to create

[9]

other

collections. Let us now briefly describe our current and future work in this area. In several applications we have implemented the run-time support for a primitive

version of collection

synchronization,

as described

currently

at the implementation

working

in

this

navigation paper.

We

and

consistent semantics [11]. As far as authoring of collections

of a generic (i.e.,

project

[21],

we have implemented

other ways to create collections. to implement authoring

a generic

in most

for

this

Hypertext

Hypermedia

supported by the Commission within

the ESPRIT

[16] Hamaka

We are grateful to the partners of these of

the

M.C., Zellweger P., “Specifying Temporar in hypermedia Documents”. In Proc. ACM

ECHT’92,

MihrIo,

Buchanan Lay-out

[3]

M.C.,

’94 Proceedings

L, “Travels

R., Rekimoto

J., “Object

“Links

in Hypermedkx

Around

a Learning

Orienteering, C’orf,

or

Toronto,

Composition

the Requirement

In Proc, ACM Hypertext’93,

Z.ellweger P., “Automatic

Mechanisms”.

Hypertext

and

Hypertext to Support Real Multimedia”. In Hypermedia, 5 (l), 1993 [18] Hardman L., Bulterman D.C.A., and Van Rossum G.,

I, Dec. 1992

Anaheim, Ca, 1993 Bush V. “As We Monthly, July 1945

ECHT

Dexter

Playback Models for Handling Multimedia Data”. In Proc. ACM Multimedia’93, Anaheim, Ca, 1993 [17] Hardman L,, Bulterman D.C.A., Van Rossum G., “The Amsterdam Hypermedia Model: Extending

Hypermedia

Buchanan Behaviour

a

In Comm, ACM,

Apr. 1988

projects

REFERENCES

[2]

“The

Rambling, Support Environment Touring”. In Proc. ACM CHI+HZ

project and to all the members Laboratory at Politecnico di Milano.

[1]

M.

System”,

In Cornm. ACM, 37 (2), Feb. 1994

[15] Hannond N, Hallison

of the European Communities

In” TX,

D. (cd.), University’ de Genbve, 1993 K., Trigg R.H., “Design Issues for

Reference Model”.

ACKNOWLEDGEMENTS

HIFI and MINERS.

’91 (S. Antonio,

Jan. 1993 Garzotto F., Mainetti L., Paolini P., “HDM2 Extending the E-R Approach to Hypermedia Application Design”. In Proc.12th Int’1 Conf on the Entity-Relationship Approach, Arlington, Tx, Dec. 1993

37(2), Feb. 1994 [14] Halatz F., Schwartz

general

environment,

This work has been partially

- A Model

Applications”.

In ACM Trans. Ofl. Znjl Syst., 11 (l), Jan. 1993 Garzotto F., Mainetti L., Paolini P, “Navigation patterns in Hypermedia Data Bases”, In Proc, 26th IEEE Int’1. Con. on System Sciences, Maui - USA,

Dexter-Based

working

more

ACM

Hypertext

Garzotto F., Paolini P., Schwabe D. “HDM - A Model Based Approach to Hypermedia Application Design”

Tsichritzis [13] Gronbaek

also all the

We are currently

version

of

Engine for Collection Based Navigation in Hypermedia Applications” - in preparation [12] Gibbs S., Breiteneder C., Tsichritzis D., “Data Modeliig of Visual Objects”, In Visual Objects,

cases we have basically been using built-in, pick-up and intentional (query-based) definitions. In the context of a specific

Design

In Journal of Organizational Computing -to appear [11] Garzotto F., Mainetti L., Paolini P., “A Run-Time

a clear and

is concerned,

the

Ca,

[10] Garzotto F., Mainetti L., Paolini P., “Navigation in Hypermedia Application Modelling and Semantics”,

are

application independent) run-time engine to support the most general version of collections. We are also defining an abstract model for it, in order to provide

Anaheim,

Dec. 1991)

we have discussed in the previous section.

and also are an important

Multimedia”93,

Garzotto F,, Paolini P., Schwabe D. “HDM

Hardman et al. [17, 18, 19], and Buchanan et al. [1, 2], can

With respect to the typical usage of collections Bases, our collections exhibit several difference~ navigation capabilities; relaxation structurq

ACM

Temporal

[19] Hardman

In Proc. ACM Multimedia’93,

“Adding

L.,

Bulterman

Time and Content

for Context”.

Seattle, Wa, 1993 D.C,A.,

Van

Rossum

to the Dexter Model”.

G., In

Comm. ACM, 37 (2), Feb. 1994 May

Think”.

In

The Atlantic

“Guided [20] Marshall C,, Presentations: How Authors

79

Tours and Make Existing

On-Line Hypertext

September 1994

Intelligible Pittsburgh,

for Readers”. In Proc. ACM Hypertext’89, PN, NOV. 1989

[21] MINERS Project ESPRIT P6552 “MINERS: An Editorial Platform for Electronic and Traditional Publishing”, Technical Annex, 1991 [22] Ogawa R., Harada H., Keneto A., “Scenario-based Hypermedk A Model and a Systems”, in Hypertext: Concepts,

Systems, and Applications, Rizk A, Streitz J. (eds.), Cambridge University Press,

N, and Andre’

1990 [23] Prabhakaran Models

for

B.,

Rahavan

Multimedia

Participation”.

In

S.V.,

“Synchronization

Presentation

Proc.

ACM

with

User

Multimedia’93,

Anaheim, Ca, 1993 [24] Trigg R.H., Weiser M., “TEXTNET A NetworkBased Approach to Text Handling”. In ACM Trans. Off. Inf Syst., 4 (l), 1986 [25] Trigg R.H., “Guided Tours and Tabletops:

Tools for

Communicating in a Hypertext Environment”. ACM Trans. Of. Infi Syst. 6 (4), 1988

In

[26] Van Dyke Parunak H. “Don’t Link Me In: Set Based Hypermedia for Taxonomic Reasoning”. In Proc. ACM Hypertext’91,

S. Antonio,

TX, Dee. 1991

[27] Van Dyke Parunak H., “Hypercubes

Grow

on Trees

(and Other Observations from the Land of Hypersets)”. In Proc. ACM Hypertext’93, Seattle,Wa, Nov.1993 [28] Zdonik S.B.,

Maier

D.

(eds),

“Reading

in

Object

Oriented Database Systems”, Introduction paper, Morgan Kaufmann Publishing, 1990, S.Mateo, CA [29] Zellweger P., “Scripted Documents: A Hypermedia In Proc. ACM Hypertext”89, Path Mechanism”. Pittsburgh, PN, NOV. 1989

ECHT ’94 Proceedings

-

80

September 1994