... different data without updating
the schema. With user-defined fields, data lacks a description of its meaning. Mislabeled
fields are worse, as the description is misleading.
• Binary fields. Some databases ... You should be suspicious of tables with
zero records.
8.3 Disguised Fields Antipattern
8.3.1 Observation
The name and documentation for a field do not indicate the kind of da...
... expertly building data models.
This book focuses on databases and not on programming, because most commercial
software is built around a database. The database representation (the data model) sets ... scope, and set the
xiv Preface
key abstractions in the software. These tasks revolve around models and often data mod-
els. The skillful use of patterns is intrinsic to building qualit...
... Spanish, and Chinese. Data can often be stored in the language of entry, but there
is a need to translate metadata, such as labels in forms and reports.
Chapter 13 covers softcoded values. The ... values can be softcoded — metadata
specifies the intended model and generic tables store the values. Softcoded values are appro-
priate for applications with uncertain data structure; softcodi...
... Area 191
An Entity is a thing with semantic meaning. Examples of Entities include a data flow in
a data flow diagram and a piece of equipment in an equipment flow diagram. An Entity can
be represented ... are helpful for some kinds of models and unnecessary for others. If a diagram
omits Ports , then connections go directly to Entities.
An EntityType is a classification of Entitie...
... chapter starts with a discussion of models and then introduces the topic of patterns.
1.1 What Is a Model?
A model is an abstraction of some aspect of a problem. Most software models are expressed
as ... combinations.
Patterns provide a higher level of building blocks than modeling primitives. Patterns are
prototypical model fragments that distill the knowledge of experts.
•...
... Software Architecture: A System of Patterns. Chichester, United Kingdom:
Wiley, 1996.
[Chen-1976] PPS Chen. The entity-relationship model—toward a unified view of data. ACM Transac-
tions on Database ... Vlissides. Design Patterns: El-
ements of Reusable Object-Oriented Software. Boston, Massachusetts: Addison-Wesley, 1995.
[Hay-1996] David C. Hay. Data Model Patterns: Conventions...
... the sequence of types in
the levels of the hierarchy.
• Simple tree. Restricts nodes to a single tree. Treats nodes the same. Use when tree de-
composition is merely a matter of data structure.
• ... context. Figure 2.11 shows an excerpt of this book’s file structure where I have kept
old copies of files from reviews. File names are unique within the context of their directory....
... branch nodes. A Tree is a hierarchy of nodes and has one node as the root.
A particular node may, or may not, be the root. You need not show Tree in a use of the tem-
plate.
A Node is either ... nodes each of which, in turn, can be a leaf node or a further branch node.
Figure 2.18 adds the constraint that a tree cannot have any cycles. (See Section 2.2.1 for
an explanation of cycles.)...