Database Reference
In-Depth Information
4
The problem of relational data exchange
The goal of this chapter is to introduce the key definitions for relational data exchange, as
well as the key problems that we are going to study - checking whether a solution exists,
constructing solutions with good properties, and using such solutions for query answering.
4.1 Key definitions
We start by revisiting the data exchange example presented in
Chapter 1
.
M
=(R
s
,
R
t
,
Example 4.1
In the example seen in
Chapter 1
, we used the mapping
Σ
st
)
in which:
(1) The source schema R
s
consists of the ternary relation
GEO(city,country,population)
and the 4-ary relation
FLIGHT(source,destination,airline,departure)
.
(2) The target schema R
t
consists of the ternary relation
ROUTES(flight#,source,destination)
and the 4-ary relations
INFO FLIGHT(flight#,departure time,arrival time,airline)
and
SERVES(airline,city,country,phone)
.
(3)
Σ
st
consists of the following source-to-target dependencies:
