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4.2.3 Method A method corresponds to a 
function or a procedure. A method is the code in 
an object that tells the object how to react when 
it receives a message with the same name as the 
method. In HyperTalk, the handlers correspond 
closely to OOP method. A Handler is associated 
with each type of message the object can receive. 
But a message is different from a method, besides 
the handler descriptions, the message also 
includes other scripts, such as card name, card 
fields, etc. 
4.2.4 Class The concept of class is the same 
as classification in object-oriented data models. 
The most important thing objects in class have in 
common is the way they react to one or more 
messages. When we define a class, each object we 
create as a member of that class is contained. 
That means that it is not necessary to send the 
messages to each single object. In HyperTalk, 
there is no strong analogue to OOP’s concept of 
classes. For example, there is no class called a 
button class to which all buttons belong and 
which has individual instances of buttons. The 
concept of card backgrounds however, comes close 
to emulating an OOP class. All cards in a stack 
with the same backgrounds have many common 
characteristics. 
4,2.5 Inheritance In a true object-oriented 
world, objects inherit behavior from their 
ancestors in an ever-expanding and descending 
chain of heredity. That implies that an object of 
a subclass reacts to the messages not only from 
the same class but also from its ancestors. There 
is also no true inheritance in HyperTalk. An 
object does not inherit behavior from its 
ancestors. But like the class in HyperTalk, we 
can copy new cards with the same backgrounds 
which can react to the same operations or have 
the same properties. When we define some 
backgrounds for a class in a stack, all objects 
in this class and its subclasses have the same 
backgrounds. However, this is not inheritance 
because the new cards of the same backgrounds are 
not the descendants of the original; both are on 
the same level of the hierarchy. According to 
inheritance in object-oriented programming, the 
operations defined specifically for a subclass 
are not applicable for objects of the 
superclasses. But in HyperTalk, if a background 
is modified or added in the card of the subclass, 
the cards of its superclasses in the same stack 
will be affected. 
4.3 Object-oriented Models in attribute database 
Geographical information systems are employed to 
store and describe the complex information and 
phenomena in the real world. The object-oriented 
data model can serve as a conceptual model. The 
classification, generalization, association and 
aggregation are used to define the classes of 
objects, to describe the relationship of the 
classes and to compose the complex objects. The 
object-oriented language such as  HyperTalk 
provides an environment to encapsulate data and 
operation in a modular, and the mechanism of 
inheritance and propagation. In technique, it has 
provided a seamless combination between Oracle 
and HyperTalk. 
4.3.1 Classification in GIS The features in 
GIS can be classified according to the 
classification criteria of GIS. Some ideas of the 
classification in object-oriented models are 
proposed here. A class corresponds to a table in 
the relational database and uses a card in 
777 
HyperTalk. The card includes some operation 
‘icons’ like select, insert, delete, etc., some 
property ’containers’ and some classification 
icons’. A column in a table corresponds to a 
container in a card. A row in a table represents 
an object (an instance).The features in GIS can 
be classified as road, building, park, water- 
system, vegetation, phone-line and so on. Fig. 8 
Shows the classifications of the features. Every 
subclass in the card GIS can be classified 
further. For example, the class building can be 
classified into residence, hotel, supermarket, 
factory, bank and so on (see Fig.9). 
Sequentially, for instance, the hotel can be 
decomposed into the classes of employer and 
room&bed are not the subclasses of the class 
hotel, and the relationship between the employees 
or room bed and the hotel is the part_of 
relation. So the properties and the operations of 
the class hotel and class building do not inherit 
them. However, the class hotel can derive the 
values from the tables of employees and room&bed. 
Fig. 10 shows the classifications of the features 
and their relationship. 
4.3.2 Generalization in GIS Several classes of 
objects with common properties and operations are 
organized to form a more general superclass. For 
example, factories, farms, supermarkets, hotels 
and restaurants have the common properties income 
and tax. They are formed into a higher level 
class business, and use a table which has the 
columns business name, income and tax. 
4.3.3 Inheritance and Propagation in GIS The 
mechanisms of inheritance and propagation are 
important in  GIS. Some simple tables are 
established in an attribute database. But the 
user sometimes needs to query the detailed 
information of an object such as a hotel. A table 
of the hotel only includes the fields identifier, 
hotel name, manager name and phone number. 
However, the user needs its more detailed 
information like its address, income, employees, 
beds and so on. Therefore, the user must 
manipulate several tables. The Oracle system has 
the function of querying multiple tables. In card 
hotel, the properties of its superclass building 
and business are inherited to it, and several 
fields that represent the properties in the hotel 
table are built singly. Sequentially, a field 
employees and two fields rooms and beds are used 
for propagation which aggregate the values in the 
table employee and room&bed. The button select 
holds the handlers of querying multiple tables 
and adding sum. When the user uses the command 
select, the select "icon" receives the message 
and sends it into the handler, and then 
manipulates the tables building, business, hotel, 
employee and room&bed. The information is put 
into the corresponding fields (see Fig. 
11).Actually, the query is divided into two 
steps. The first, querying multiple tables hotel, 
building and business gets the information of 
hotel and its superclass building and business. 
The second, according to the name of the hotel 
shown in the field, querying the tables employee 
and room&bed of this hotel, gets the sums of the 
corresponding columns. If HyperTalk were not used 
we could not do the second step. Here HyperTalk 
send a message name, which is obtained from the 
first step, to the field of hotel name, then 
query the tables corresponding to this hotel name 
because each hotel use an employee table and a 
room bed table. This is an advantage of 
HyperTalk, because an object or "icon" can hold 
several handlers.