03 Database Models PART3 — Transcript

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1. 0:00in this video lecture we will learn that
2. 0:02using levels of abstraction
3. 0:04can be very helpful in integrating
4. 0:07multiple
5. 0:07and sometimes conflicting views of data
6. 0:10at different levels of an
7. 0:11organization so let's start
8. 0:17in the early 1970s the american national
9. 0:20standards institute or ansai
10. 0:22standards planning and requirements
11. 0:24committee or spark
12. 0:26defined a framework for data modeling
13. 0:28based on degrees of data abstraction
14. 0:31the resulting onsite spark architecture
15. 0:34defines
16. 0:35three levels of data abstraction
17. 0:37external
18. 0:38conceptual and internal you can use this
19. 0:42framework to better understand database
20. 0:45models
21. 0:47as given here in figure 2.6
22. 0:50this is a framework that has been
23. 0:52expanded with the addition of physical
24. 0:54model
25. 0:55to explicitly address physical level
26. 0:57implementation details
27. 0:59of the internal model
28. 1:05the external model is the end user's
29. 1:08view of the data environment
30. 1:10the term end users refers to people
31. 1:13who use the application programs to
32. 1:16manipulate the data and generate
33. 1:18information end users usually operate
34. 1:21in an environment in which an
35. 1:24application has a specific business unit
36. 1:26vocals
37. 1:27companies are generally divided in
38. 1:29several business units such as
39. 1:32sales finance and marketing each
40. 1:35business unit is subject to specific
41. 1:37constraints and requirements
42. 1:39and each one uses a subset of the
43. 1:42overall data in the organization
44. 1:44therefore the end users within those
45. 1:47business units
46. 1:48view their data subsets a separate form
47. 1:52or external to other units within the
48. 1:55organization
49. 1:56because data is being modeled your
50. 1:59diagrams
51. 2:01will be used to represent the external
52. 2:03views
53. 2:04a specific representation of an external
54. 2:06view is known as
55. 2:08an external schema
56. 2:13figure 2.7 presents the external schemas
57. 2:16for two
58. 2:17tiny college business units student
59. 2:20registration and class scheduling
60. 2:22each external schema includes
61. 2:24appropriate entities relationships
62. 2:27processes and constraints imposed by the
63. 2:30business you need
64. 2:31also note that although the application
65. 2:33views are isolated from each other
66. 2:36each view shares a common entity with
67. 2:39the other view
68. 2:40for example the registration scheduling
69. 2:44external schemas share the entities
70. 2:47class
71. 2:47and course note the er is represented
72. 2:51in this figure a professor may teach
73. 2:55many classes and each class is thought
74. 2:57by only one professor there is a one
75. 3:00is too many relationship between
76. 3:03professor and class
77. 3:06a class may enroll many students and
78. 3:08each student may enroll
79. 3:10in many classes thus creating
80. 3:14a many is to menu relationship between
81. 3:16student and class
82. 3:18each course may generate many classes
83. 3:22but each class references a single
84. 3:25course
85. 3:25for example there may be several classes
86. 3:28or sections of a database course
87. 3:30that have a course code of cis420
88. 3:35finally a class requires one room but a
89. 3:38room may be scheduled for many classes
90. 3:41there is one is to menu relationship
91. 3:43between room
92. 3:44and class
93. 3:52a conceptual model represents a global
94. 3:54view of the entire database by the
95. 3:56entire organization
96. 3:58a conceptual schema is the basis for the
97. 4:01identification and high level
98. 4:03description
99. 4:04of the main data objects logical design
100. 4:08is the task of creating conceptual data
101. 4:10model
102. 4:11conceptual model advantages includes
103. 4:14macro level view of data environment
104. 4:16and software and hardware independency
105. 4:23a simplified version of the internal
106. 4:25model for tiny college is showing
107. 4:27in figure 2.9
108. 4:34the internal model representing database
109. 4:37as seen by the dbms mapping conceptual
110. 4:39model
111. 4:40to the bbms it has internal schema
112. 4:44which has the specific representation of
113. 4:46an internal model
114. 4:48using the database constructs supported
115. 4:50by the chosen database
116. 4:52logical independence is the changing of
117. 4:55internal model without affecting the
118. 4:58conceptual model
119. 5:00and the hardware independence means
120. 5:02unaffected
121. 5:04by any type of computer in which the
122. 5:06software is installed
123. 5:12the physical model operates at the
124. 5:14lowest level of obstruction
125. 5:16describing the way data is saved on a
126. 5:18storage media
127. 5:20such as magnetic solid state or optical
128. 5:23media
129. 5:24the physical model requires the
130. 5:25definition of both the physical storage
131. 5:28devices
132. 5:29and the physical access methods required
133. 5:32to reach the data within those
134. 5:33storage devices making it both software
135. 5:36and hardware dependent
136. 5:39although the relational model does not
137. 5:41require the designer to be concerned
138. 5:43about the data's physical storage
139. 5:45characteristics
140. 5:46the implementation of a relational model
141. 5:49may require
142. 5:50physical level fine tuning for increased
143. 5:53performance
144. 5:54fine tuning is especially important when
145. 5:58very large databases are installed in a
146. 6:00mainframe environment
147. 6:02when you can change the physical model
148. 6:04without affecting the
149. 6:06internal model that is physical
150. 6:09independence
151. 6:14the levels of data obstruction are
152. 6:16summarized in table 2.4
153. 6:20for external model it has
154. 6:23high degree of obstruction the focus is
155. 6:27the end user views
156. 6:29and it is hardware and software
157. 6:31independent
158. 6:33conceptual model has a degree of
159. 6:36obstruction
160. 6:37of medium to high and its focus
161. 6:41is for global view of data it's also
162. 6:44hardware and software independent
163. 6:48for internal model it has medium to low
164. 6:53degree of obstruction and its focus
165. 6:56is on specific database model
166. 6:59it is hardware independent
167. 7:02while for the physical model the degree
168. 7:05of abstraction is
169. 7:07low and its focus its
170. 7:10storage and access methods while
171. 7:14neither hardware nor software
172. 7:17is independent of it
173. 7:24to summarize module one topic three
174. 7:27a data model is an abstraction of a
175. 7:30complex real-world data
176. 7:32environment there are many types of data
177. 7:35models
178. 7:36hierarchical network relational
179. 7:39object-oriented
180. 7:40extended relational data models
181. 7:44and data modeling requirements are a
182. 7:46function of different data views
183. 7:49and the level of data obstruction
184. 7:54we are now done with topic two data
185. 7:56models
186. 7:57next meeting we will discuss entity
187. 8:00relationship models
188. 8:01another advanced data model please don't
189. 8:04forget to answer our exercise 3
190. 8:07thank you