PATTERNS OF DATA MODELING- P15 pptx

Node tablenode ID node Name Connection table connec tionID node ID edge ID source OrSink Figure 3.32 Connection directed graph: Populated tables.. 3.4.5 ExampleThe connection template is

Node table

node

ID

node

Name

Connection table connec

tionID

node ID

edge ID

source OrSink

Figure 3.32 Connection directed graph: Populated tables

Edge table edge

ID

edge Name

51 c

52 d

53 e

54 f

55 g

56 h

57 i

Connection table (cont) connec

tionID

node ID

edge ID

source OrSink

B c

d

e

F

A

f

g

Figure 3.33 Connection directed graph: Populated tables

Node table

node

ID

node

Name

Connection table connec

tionID

node ID

edge ID

source OrSink

Edge table

edge

ID

edge Name

61 r

62 s

63 t

Connection table (cont) connec

tionID

node ID

edge ID

source OrSink

Y X

r s t

3.4.5 Example

The connection template is sometimes helpful for representing directed graphs as Figure 3.34 illustrates A manufacturing plant can have a variety of equipment that is connected by piping Nozzles connect piping to equipment and have a direction of normal fluid flow

3.5 Simple DG Changing over Time Template

There are two templates for directed graphs that can change over time The first (this section)

is based on the simple directed graph The second (next section) is based on the node and edge directed graph It is also possible to extend the connection template for variations over time, but I have never seen it used in practice

3.5.1 UML Template

The template for simple directed graphs that change over time (Figure 3.35) is similar to the tree template in Section 2.5 Figure 3.35 separates an entity from its directed graph position (node) because the timeline for an entity can differ from that of its involvement in a graph

A DG (directed graph) is a set of nodes and a set of directed edges that connect nodes.

(Note: in a directed graph all the nodes do not have to be connected.) You need not show DG

2

Figure 3.34 Connection directed graph: Equipment and piping model

Nozzle

sourceOrSink

ManufacturingPlant

1

*

Figure 3.35 Simple directed graph changing over time: UML template

Use when edges are unimportant and history must be recorded

root

{Each node has at least one parent except for root nodes.}

0 1

<Node>

effectiveDate expirationDate

<Binding>

effectiveDate expirationDate

<DG>

<Entity>

effectiveDate expirationDate

<NodeLink>

effectiveDate expirationDate

*

*

1 1 parent child

*

{There cannot be any cycles.}

in a use of the template A Node is a position within a directed graph The distinction

be-tween parent and child causes the sense of direction that effects directed edges.

Figure 3.35 adds the constraint that each node has at least one parent except for root nodes (The template itself is more permissive and lacks this constraint.) In general, a

direct-ed graph may have cycles but this template disallows them (A cycle starts at a node and after traversing a series of edges reaches the starting node.) Since this template is based on a tree template, it doesn’t make sense to permit cycles

This template is already complex, so it is best to handle node names in a simple manner Each node has a globally unique name and there is no provision to vary node name by

con-text The effective and expiration dates permit Node and Entity data to vary over time.

3.5.2 IDEF1X Template

Figure 3.36 restates Figure 3.35 with the IDEF1X notation The following are foreign keys:

dgID references DG, nodeID references Node, entityID references Entity, parentNodeID ref-erences Node, and childNodeID refref-erences Node.

In Figure 3.36 the node name can change over time (three part candidate key—node-Name + effectiveDate + expirationDate), but the node name could also be invariant over time (candidate key of nodeName alone) Note that the handling of time reflects a limitation of

relational DBMSs It would be better to use time intervals but most relational DBMSs only support points in time

3.5.3 SQL Queries

Figure 3.37 and Figure 3.38 show SQL queries for common traversals of the template The colon prefix denotes variable values that must be provided for each query

bindingID

Binding

effectiveDate expirationDate nodeID (FK) entityID (FK)

nodeID

Node

nodeName (AK1.1) effectiveDate (AK1.2) expirationDate (AK1.3)

entityID

Entity

effectiveDate expirationDate

nodeLinkID

NodeLink

effectiveDate expirationDate parentNodeID (FK) childNodeID (FK)

Figure 3.36 Simple directed graph changing over time: IDEF1X template

dgID (FK) dgID

DG

Figure 3.37 Simple directed graph changing over time: SQL query

Find the parents for a child node

SELECT Parent.nodeID AS parentNodeID,

Parent.nodeName AS parentNodeName

FROM Node AS Child

INNER JOIN NodeLink AS NL ON Child.nodeID = NL.childNodeID INNER JOIN Node AS Parent ON NL.parentNodeID = Parent.nodeID WHERE Child.nodeID = :aChildNodeID AND

(Child.effectiveDate IS NULL OR

:aDate >= Child.effectiveDate) AND

(Child.expirationDate IS NULL OR

:aDate <= Child.expirationDate) AND

(NL.effectiveDate IS NULL OR

:aDate >= NL.effectiveDate) AND

(NL.expirationDate IS NULL OR

:aDate <= NL.expirationDate) AND

(Parent.effectiveDate IS NULL OR

:aDate >= Parent.effectiveDate) AND

(Parent.expirationDate IS NULL OR

:aDate <= Parent.expirationDate)

ORDER BY Parent.nodeName;

Figure 3.38 Simple directed graph changing over time: SQL query

Find the children for a parent node

SELECT Child.nodeID AS childNodeID,

Child.nodeName AS childNodeName

FROM Node AS Child

INNER JOIN NodeLink AS NL ON Child.nodeID = NL.childNodeID INNER JOIN Node AS Parent ON NL.parentNodeID = Parent.nodeID WHERE Parent.nodeID = :aParentNodeID AND

(Child.effectiveDate IS NULL OR

:aDate >= Child.effectiveDate) AND

(Child.expirationDate IS NULL OR

:aDate <= Child.expirationDate) AND

(NL.effectiveDate IS NULL OR

:aDate >= NL.effectiveDate) AND

(NL.expirationDate IS NULL OR

:aDate <= NL.expirationDate) AND

(Parent.effectiveDate IS NULL OR

:aDate >= Parent.effectiveDate) AND

(Parent.expirationDate IS NULL OR

:aDate <= Parent.expirationDate)

ORDER BY Child.nodeName;

3.5.4 Sample Populated Tables

Figure 3.39 shows tables populated with data for the simple directed graph changing over

time The values of the IDs are arbitrary, but internally consistent A null effectiveDate means that a Node applies indefinitely from the past A null expirationDate means that a Node applies indefinitely into the future In accordance with the template, there are no

ex-plicit edges and edges are represented via the coupling between nodes

As in Section 3.1, the template cannot express directed graphs with multiple edges

be-tween a pair of nodes For brevity, the Node table omits the dgID column This simple ex-ample does not populate Binding and Entity.

3.5.5 Example

Figure 3.40 revisits the example from Section 2.5 The management structure can be a ma-trix, instead of a simple hierarchy; then a person can report to more than one manager at the

Directed graph, 1 July 2000 0100

Node table

node

ID

node

Name

effective

Date

expiration Date

2000 0100

2000 0300

Directed graph, 1 July 2000 0300

NodeLink table node

link ID

effective Date

expiration Date

parent Node ID

child Node ID

2000 0100

7 1 July

2000 0300

Figure 3.39 Simple directed graph changing over time: Populated tables

N M

L K

J

L K

J

X