Franca Garzotto, Luca Mainetti, Paolo Paolini. Politecnico di Milano - Department of Electronics and Information. Piazza Leonardo & Vinci 32-20129. Milano - ...
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
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ECHT ’94 Proceedings
-
80
September 1994
