Basic Concepts of Entity-Relationship Model — Transcript

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1. 0:03[Music]
2. 0:06hello everyone
3. 0:07and welcome to the course of dbms in
4. 0:10this video
5. 0:11we're going to look into the basic
6. 0:12concepts of entity relationship
7. 0:15model or otherwise called the er model
8. 0:19so basically in this video we will be
9. 0:20looking into few important terminologies
10. 0:23in relation to the er model the entity
11. 0:26relationship
12. 0:27model or the er model describes data
13. 0:30as entities attributes and relationships
14. 0:34in this video we will be mainly focusing
15. 0:36on entities and attributes
16. 0:38and in the later videos we will be
17. 0:40looking into the concept of
18. 0:42relationships now what is an entity
19. 0:45it is a thing in the real world with an
20. 0:48independent
21. 0:49existence that is it is a thing or an
22. 0:51object that has its own identity or that
23. 0:54can be
24. 0:55identified easily an entity may be an
25. 0:58object with physical existence like for
26. 1:01example
27. 1:02a house person an employee
28. 1:05etc or it can be objects with a
29. 1:07conceptual
30. 1:08existence like for example course
31. 1:11job etc so this is what an entity is
32. 1:15next let us see what attributes are
33. 1:18attributes
34. 1:19are properties that describe the
35. 1:22entities
36. 1:23for example if i have an entity person
37. 1:26the properties that would describe
38. 1:27this particular entity would be name age
39. 1:31address phone number etc so these are
40. 1:35called as
41. 1:35attributes of this entity in our further
42. 1:38videos
43. 1:39we will learn about each of the symbols
44. 1:41that we have used here
45. 1:42and also all the other symbols that we
46. 1:44use in the er diagram
47. 1:46now let's look into the several types of
48. 1:48attributes in the er model with examples
49. 1:52first let us see what composite
50. 1:53attributes and simple attributes are
51. 1:56composite attributes are attributes that
52. 1:58can be divided into further parts
53. 2:01whereas simple attributes are attributes
54. 2:03that cannot be divided further
55. 2:06an example of a composite attribute is
56. 2:08name
57. 2:09this attribute can be divided into
58. 2:11further parts first name
59. 2:13middle name and last name an example of
60. 2:16a simple
61. 2:16attribute is weight this attribute
62. 2:19cannot be further divided
63. 2:21other examples could be salary a
64. 2:23person's age
65. 2:24etc so this is about composite and
66. 2:27simple attributes
67. 2:29next we have the single valued
68. 2:31attributes and multi-valued attributes
69. 2:34single valued attributes are attributes
70. 2:36that have a single value
71. 2:38or just one value for a particular
72. 2:40entity
73. 2:41whereas multi-valued attributes are
74. 2:43attributes that can have
75. 2:45a set of values for a particular entity
76. 2:48an example for a single valued attribute
77. 2:50is age
78. 2:52a particular person can have only a
79. 2:54single value for this
80. 2:55particular attribute so age is a single
81. 2:59valued attribute of a person
82. 3:01examples of multi-valued attributes are
83. 3:04college degree
84. 3:05languages known etc a particular person
85. 3:09can have more than one college degree
86. 3:11and can also know more than one language
87. 3:14since these attributes can have a set of
88. 3:16values for a particular entity
89. 3:18it is called as a multi-valued attribute
90. 3:20of a person
91. 3:22so these are about single valued
92. 3:24attributes and multi-value attributes
93. 3:26next let us see what derived attributes
94. 3:29and stored attributes are
95. 3:31derived attributes are attributes that
96. 3:33can be derived from
97. 3:35other attributes whereas stored
98. 3:37attributes
99. 3:38are attributes from which the value of
100. 3:41other attributes
101. 3:42are derived an example of a derived
102. 3:44attribute
103. 3:45is age since age can be derived from
104. 3:48date of birth this is called a derived
105. 3:51attribute
106. 3:52whereas date of birth or birth date of a
107. 3:54person
108. 3:55is a stored attribute because from this
109. 3:58attribute
110. 3:59we can derive age of a person so this is
111. 4:01a stored attribute from which the value
112. 4:04of
113. 4:04other attributes are derived next let us
114. 4:07see what are complex
115. 4:09attributes a complex attribute has
116. 4:12multi-valued and composite components in
117. 4:15it
118. 4:15we have already seen earlier in this
119. 4:17video what multi-valued and composite
120. 4:19attributes are
121. 4:20so a complex attribute has both
122. 4:22multivalued and composite components
123. 4:25here in the complex attribute a
124. 4:27multi-valued attribute is represented
125. 4:29within curly brackets
126. 4:31and composite attributes are represented
127. 4:34within round brackets or paranthesis
128. 4:37this is an example of a complex
129. 4:38attribute here college degrees
130. 4:41which is represented within curly
131. 4:43brackets is a multi-valued attribute
132. 4:45because one person can have more than
133. 4:47one
134. 4:48degree and within the parenthesis is the
135. 4:50composite attribute
136. 4:52so this is about complex attributes next
137. 4:54we're going to learn about
138. 4:56null values null is something which is
139. 4:59not
140. 4:59applicable or unknown so when does null
141. 5:03value mean not applicable in some cases
142. 5:06an entity might not have an
143. 5:07applicable value for an attribute like
144. 5:10for example if i have an
145. 5:12attribute college degree this attribute
146. 5:15applies only to persons with a college
147. 5:17degree
148. 5:18or if i have an attribute say the
149. 5:19landline number this attribute again
150. 5:22applies only to persons who has a
151. 5:23landline
152. 5:24so a person who has no college degree
153. 5:26will have null
154. 5:27for the attribute college degree and a
155. 5:29person who has no landline phone
156. 5:32will have null for the attribute
157. 5:34landline number
158. 5:35so in this particular case the meaning
159. 5:37of null is not
160. 5:38applicable null can also be used when we
161. 5:41don't know the value of an attribute
162. 5:44like for example if we don't know the
163. 5:46phone number of a particular entity here
164. 5:48say jeremy then that particular value of
165. 5:50the attribute would be
166. 5:52null so in this case the meaning of null
167. 5:54is unknown
168. 5:55the unknown category of null can be
169. 5:58further classified into two cases
170. 6:00the first case is when the value exists
171. 6:03but it is missing
172. 6:04like for example the age of joshua
173. 6:07exists but it is missing so that value
174. 6:10would be null
175. 6:11the second case is when it is not known
176. 6:13if the value
177. 6:14exists or not like for example if you
178. 6:18don't know whether the student jeremy
179. 6:19has a phone number or not
180. 6:21in that case the value of the attribute
181. 6:23phone number would be null
182. 6:25hope you understood what null values are
183. 6:27the next terminology that we are going
184. 6:29to learn
185. 6:29is entity type what is entity type
186. 6:33it is a collection of entities that have
187. 6:35the same
188. 6:36attributes example of an entity type is
189. 6:39student
190. 6:40so here each record in this table is an
191. 6:43entity
192. 6:44we have harry jeremy and joshua as the
193. 6:47entities
194. 6:48these entities share the same attribute
195. 6:50that is
196. 6:51age and they belong to the entity type
197. 6:53student
198. 6:54so an entity type is a collection of
199. 6:57entities that have the same
200. 6:58attributes now what is an entity set
201. 7:02it is a collection of entities of a
202. 7:04particular entity type at a point in
203. 7:06time
204. 7:07if i say i need students whose age is
205. 7:10between 19 and 23
206. 7:12so at that particular point in time all
207. 7:14the students with age between 19 and 23
208. 7:17is an entity set next let us see what a
209. 7:20key attribute
210. 7:21is a key attribute of a particular
211. 7:24entity type
212. 7:25is that attribute that is capable of
213. 7:28identifying each
214. 7:29entity uniquely for example role number
215. 7:32of a student
216. 7:34now in this table with entity type
217. 7:36student i have two
218. 7:37students with the same name and also the
219. 7:40same
220. 7:40age if i have to identify this
221. 7:43particular student uniquely
222. 7:45i can identify her by her student id or
223. 7:48role number
224. 7:49because no two students can share the
225. 7:51same role number in a particular class
226. 7:53so the attribute role number or student
227. 7:56id is a key attribute
228. 7:58to identify a student uniquely next what
229. 8:01is
230. 8:01value set of attributes value set of
231. 8:04attributes is a set of values that can
232. 8:06be assigned to a particular attribute
233. 8:09for example if the range allowed for the
234. 8:11age of an
235. 8:12employee is between 22 and 60 then we
236. 8:15can specify the value set
237. 8:17of the age attribute of an employee as a
238. 8:19set of integer numbers between
239. 8:2122 and 60. so that is called as a value
240. 8:24set
241. 8:25so these are the few important
242. 8:26terminologies that we need to know in
243. 8:28relation to the er model
244. 8:30with this we come to the end of this
245. 8:32video hope you have understood the
246. 8:34definition of each of these
247. 8:35terminologies
248. 8:36thank you
249. 8:40[Music]
250. 8:48you