vi ;;Quote: information may be too ambiguous and subjective to be embodied in a computer

vii ;;Quote: the real mystique of computers is their elaborate behavior from limited capabilities

viii ;;Quote: problems aggravated in computerized data bases since fewer conversations about the data

1 ;;Quote: a database models a small, finite subset of the real world

1 ;;Quote: database entities correspond to real entities

2 ;;Quote: information in a database is part of a communication process between people; with translations to and from formal languages

2 ;;Quote: resemblance between a database's contents and the original information depends on a common understanding of what references mean

3 ;;Quote: when are two things instances of the same thing

3 ;;Quote: in a bibliography, each book is an entity; in a library each copy of book is an entity

4 ;;Quote: a manual may be a 'book' in one library, but not a book in another (because it has a soft cover)

5 ;;Quote: the boundaries and extent of a classification can be arbitrary

6 ;;Quote: words are ambiguous because we must use a finite set to communicate a non-denumerable set of concepts

12 ;;Quote: in a mystery, the murderer and butler are separate entities; afterwards they are the same

13 ;;Quote: there is not a natural set of categories; a system defines its categories

13 ;;Quote: the same piece of information can be a category, an attribute, or a relationship; e.g., parents and children

13 ;;Quote: a person on leave may be an employee for benefits but not for payroll

17 ;;Quote: even though a database doesn't model reality, it is still useful

19 ;;Quote: a database models the way people process information about reality

25 ;;Quote: with an integrated database, new applications can borrow data already collected for other applications

25+ ;;Quote: changes in an integrated database are automatically made everywhere

28 ;;Quote: in traditional databases, data files and their descriptions are stored separately

31 ;;Quote: data which can be extracted from a system is not necessarily stored in the system

32 ;;Quote: the meaning of a field in a data record is usually implicit; e.g., joe smith and 95

32 ;;Quote: a database model is how users get to know and agree upon the meaning of data items

33 ;;Quote: list test for existence: if symbol on a list, then it exists

34 ;;Quote: syntactic checks for existence: a symbol is numeric, alphabetic, fixed length

34 ;;Quote: syntactic test of existence works for numbers, but not for strings, e.g., addresses

34 ;;Quote: correspondence between database model and real world is rather ad hoc

38 ;;Quote: can't represent a thing by its description; due to its relationships to other things

39 ;;Quote: representations should map one-to-one with real things

39 ;;Quote: linked representations and the existence of representations is the fundamental basis for representing information

40 ;;Quote: information associated with a representative must be asserted explicitly

41 ;;Quote: an information system is for entering and extracting information about entities

41 ;;Quote: a person has many names

42 ;;Quote: a name can be meaningless unless you know its category, e.g., Colt

43 ;;Quote: a person's name may have several correct spellings

43 ;;Quote: in Hawaii, people often use first few syllables of long last names

47 ;;Quote: qualified names resolves ambiguities by defining context; scope can be nested

49 ;;Quote: often things do not have individual, unique names, e.g., a nail

50 ;;Quote: qualified names, e.g., an employee's children, has problems of uniqueness, singularity, no qualifier, changing qualifier

53 ;;Quote: names do change

53 ;;Quote: how and how long should you handle references to old names or synonyms

54 ;;Quote: when versions are available, is it one object (the current version) or many versions

54 ;;Quote: a surrogate stands for a real thing within a system; its symbols can be different

55 ;;Quote: use objects and links to represent things; use character strings for description and communication

55 ;;Quote: with surrogates, symbolic names can be described independently of real objects

55 ;;Quote: a thing object is a node on a graph; its label may be changed, deleted, or duplicated

56 ;;Quote: names can have different relationships to things; e.g., legal name, maiden name, descriptive name

56 ;;Quote: a particular day is a single concept, but its names come in various forms

56 ;;Quote: by separating objects and names can have different types of names for the same thing, e.g., legal name and employee number

56 ;;Quote: with surrogates, can avoid confusing assertions about real things, about names, and about relationships

57 ;;Quote: in ordinary communication, the ability to stretch and modify meanings is essential

59 ;;Quote: a fact consists of identifying a relationship between surrogates

59 ;;Quote: surrogates are globally unique

59 ;;Quote: surrogates are information free; they do not imply additional information

59 ;;Quote: surrogates are atomic, unstructured units

59 ;;Quote: with surrogates, a fact is an association of surrogates that correspond to objects in the fact

60 ;;Quote: when are two names the same; equality testing by match, surrogate, list, and procedural

60 ;;Quote: in the match test, two names are the same only if they are identical

60 ;;Quote: in the surrogate test, two names are the same only if the reference the same surrogate

60 ;;Quote: in the list test, two names are the same if they occur on the same list of synonyms

60 ;;Quote: in the procedural test, two names are the same if a procedure says so

60 ;;Quote: if aliases are supported, which name is returned in answering a question

63 ;;Quote: almost everything in an information system is a relationship

63 ;;Quote: a relationship is a set of associations between things for a given reason

63 ;;Quote: the name of a relationship is a statement of a reason for an association

63 ;;Quote: an important part of a relationship is the reason for an association

64 ;;Quote: a relationship could be between an object and a set of objects, but Kent does not pursue this option

64 ;;Quote: a domain is the set of things that can occur in a given role of a relationship

65 ;;Quote: a relationship is specified by a set of roles; the degree of a relationship is the set's size

65 ;;Quote: a database model should allow arbitrary combinations of constraints on relationships

67 ;;Quote: a role can be constrained to a single domain, several domains, or unconstrained

66 ;;Quote: a relationship direction can map one to one (simple) or one to many (complex)

68 ;;Quote: even though both roles of a relationship can have the same domain, a thing may or may not be related to itself

68 ;;Quote: a relationship may be optional or mandatory for all objects in a domain

68 ;;Quote: a system may allow only one relationship between each pair of domains

70 ;;Quote: a relationship may be transitive

70 ;;Quote: a relationship may be symmetric; but such relationships are seldom supported

71 ;;Quote: a relationship can be anti-symmetric

71 ;;Quote: a relationship may be composed from other relationships

71 ;;Quote: a relationship may be a subset of another relationship

71 ;;Quote: a one-many relationship may have a maximum size

72 ;;Quote: a relationship instance may have attributes or relationships of its own

72 ;;Quote: a system should be able to list the relationships for an object or a pair of objects

72 ;;Quote: a relationship may have no name, one name, or a name for each direction

75 ;;Quote: every computable procedure represents a relationships

75 ;;Quote: an ordering between objects is a computed relationship

76 ;;Quote: even though uncle is derived from father and brother, sometimes only know the uncle relationship

76 ;;Quote: computed relationships are not modifiable; instances can be infinite, without attributes or relations

77 ;;Quote: much of information is the attributes of things

79 ;;Quote: attributes and relationships are the same kind of information

80 ;;Quote: a value, e.g., 'six feet', is an entity with many representations

82 ;;Quote: categories and attributes are the same kind of information

85 ;;Quote: things are classified into types for naming scope, validity constraints, and relationship domains; groups are mutually exclusive

88 ;;Quote: types should be non-exclusive

90 ;;Quote: minimal set predicate: the set of things having relationship x to object y

90 ;;Quote: a type is the abstract idea of a set (its intension), not its contents

90 ;;Quote: traditional set theory defines sets by their contents -- not relevant to types

91 ;;Quote: a set can be object that is related to its members

93 ;;Quote: a model or world view is a basic system of constructs used to describe reality

93 ;;Quote: a model shapes and limits our view of reality; it can distort reality to make it fit the view

94 ;;Quote: existing database models are highly structured, rigid, and simplistic

95 ;;Quote: corporations are defining their database schemas; this will be a major asset

97 ;;Quote: some authors equate signs with information, but lose the meaning of that information

98 ;;Quote: hierarchical, relational, and network models are variations of the data record model