Databases Reference
In-Depth Information
4 Template Generalisation
Whether created manually or automatically, templates are usually based on
examples of “interesting” phrases. These phrases may be identified by hand
(e.g. by a domain expert) or automatically (e.g. by information retrieval meth-
ods). These phrases are then used as “seeds” to help define more general
templates. In this framework we will follow this “seed phrase” approach, and
assume that we have some suitable phrases. We show how a wide range of
templates can be created from each seed phrase. We first discuss how terms
can be created and generalised, and then expand this to template creation
and generalisation (Sect. 4.2).
4.1 Creating and Modifying Single Template Elements
We now bring together several concepts discussed above, and define functions
that create and generalise template elements. This leads onto a discussion of
creating and modifying entire templates.
Definition 16.
Given a literal, we want to create a new template element,
which is simply a set containing the literal. We define the trivial function
initialise for this purpose: initialise
(
λ
)=
{
λ
}
.
Have created a template element, we can then modify it. We now define
a function that modifies any given template element to produce a new set
of template elements that is at least as general as the element given. This is
based on the notion of superset ordering (Sect. 3.1) in that the new template
elements match a superset of the literals matched by the original template
element. Furthermore, the new set of elements belongs to a specified category
which is different from the category of the source element.
Definition 17.
We define a function to create a more general set of template
elements from a given template element, such that all of the terms in each
new template element are members of a specified category. Given a template
element T
=
of category κ and given a target category κ
{
t
1
,t
2
,...,t
|T |
}
=
κ,
we create a set of template elements {T
1
,T
2
,...,T
n
}:
generalise
(
T,κ
)=
T
|
T
=
t
1
,t
2
,...,t
m
}
,andt
1
,t
2
,...,t
m
∈
κ
,and
{
t
i
∈
T
,
µ
(
t
i
)
∀
|
∩
µ
(
t
)
|≥
1
,and
t∈T
µ
(
t
)
, and there is no set
t
p
...t
q
}
µ
(
t
)
⊆
{
t
∈T
t∈T
µ
(
t
j
)
.
T
and
t∈T
q
t
p
...t
q
}⊂
such that
{
µ
(
t
)
⊆
j
=
p
