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Databases Final
Week 4
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Cards (17)
Data structure
The most
fundamental
and
building block
concept in database design
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Data
structure
A good
knowledge
of data structures is a must to design and
develop efficient
software systems
The way we store, organize, and group data is important for an
efficient
database system
The way we
structure
data in relation to other elements (to map these
relationships
in a structured way to represent the data)
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Examples
of well
structured data
Dictionary
Google Maps
Relational Data
Commercial database systems
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Hierarchical
data structure
Traditional method, still popular today but with
limitations
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Hierarchical
data structure
Each node may have
zero-or-more
children
Each child has
one-and-only-one
parent
Root node (top
node
) has no parent
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Hierarchical
data structure cannot support
many-to-many
relationships
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File system shortcuts can overcome
hierarchical limitations
but make the system
disorganised
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Advantages
of
hierarchical
data structure
Clean
and
logical
Fast
to navigate and
search
Little duplication even of
meta
(
descriptive
) data
Everything
is in its place and there is a place for
everything
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Disadvantages
of hierarchical data structure
Rarely models the
real
world
Often needs lots of
workarounds
(that are complicated)
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Set
theory
A more flexible solution to
structure
data
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Set
theory data structure
Items of data (nodes) can belong to
zero-or-more
sets
Sets can contain
zero-or-more
data items
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Set
operations
1. Union
2. Intersection
3.
Set Difference
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Hierarchical
data structure
Cannot support
many-to-many
relationships
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Set
theory data structure
Supports many-to-many
relationships
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Union of
two
sets contains all items that are a member of either or both sets
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Intersection
of
two
sets contains only the items that are members of both sets
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Set difference
contains the items that are in one set but not the other
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