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SECTION 11 / 13
Subtypes: narrower rules for specific fields
On this page 5 headings
A subtype narrows a broader type to suit a particular purpose. It can restrict both the allowed values and the operations. This makes the intended meaning of a field clearer.
YOUR COURSE DATA · TRY IT HERE
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BhuvaneshMaths 68 · Erode
- CardNo
- 0
- Name
- Bhuvanesh
- Gender
- M
- DateOfBirth
- 7 Nov
- CityTown
- Erode
- Mathematics
- 68
- Physics
- 64
- Chemistry
- 78
- Total
- 210
HarishMaths 62 · Salem
- CardNo
- 1
- Name
- Harish
- Gender
- M
- DateOfBirth
- 3 Jun
- CityTown
- Salem
- Mathematics
- 62
- Physics
- 45
- Chemistry
- 91
- Total
- 198
ShashankMaths 57 · Chennai
- CardNo
- 2
- Name
- Shashank
- Gender
- M
- DateOfBirth
- 4 Jan
- CityTown
- Chennai
- Mathematics
- 57
- Physics
- 54
- Chemistry
- 77
- Total
- 188
RidaMaths 42 · Chennai
- CardNo
- 3
- Name
- Rida
- Gender
- F
- DateOfBirth
- 5 May
- CityTown
- Chennai
- Mathematics
- 42
- Physics
- 53
- Chemistry
- 78
- Total
- 173
RitikaMaths 87 · Madurai
- CardNo
- 4
- Name
- Ritika
- Gender
- F
- DateOfBirth
- 17 Nov
- CityTown
- Madurai
- Mathematics
- 87
- Physics
- 64
- Chemistry
- 89
- Total
- 240
AkshayaMaths 71 · Chennai
- CardNo
- 5
- Name
- Akshaya
- Gender
- F
- DateOfBirth
- 8 Feb
- CityTown
- Chennai
- Mathematics
- 71
- Physics
- 92
- Chemistry
- 84
- Total
- 247
SameerMaths 81 · Ambur
- CardNo
- 6
- Name
- Sameer
- Gender
- M
- DateOfBirth
- 23 Mar
- CityTown
- Ambur
- Mathematics
- 81
- Physics
- 82
- Chemistry
- 87
- Total
- 250
AdityaMaths 84 · Vellore
- CardNo
- 7
- Name
- Aditya
- Gender
- M
- DateOfBirth
- 15 Mar
- CityTown
- Vellore
- Mathematics
- 84
- Physics
- 92
- Chemistry
- 76
- Total
- 252
SuryaMaths 74 · Bengaluru
- CardNo
- 8
- Name
- Surya
- Gender
- M
- DateOfBirth
- 28 Feb
- CityTown
- Bengaluru
- Mathematics
- 74
- Physics
- 64
- Chemistry
- 51
- Total
- 189
ClarenceMaths 63 · Bengaluru
- CardNo
- 9
- Name
- Clarence
- Gender
- M
- DateOfBirth
- 6 Dec
- CityTown
- Bengaluru
- Mathematics
- 63
- Physics
- 88
- Chemistry
- 73
- Total
- 224
KavyaMaths 64 · Chennai
- CardNo
- 10
- Name
- Kavya
- Gender
- F
- DateOfBirth
- 12 Jan
- CityTown
- Chennai
- Mathematics
- 64
- Physics
- 72
- Chemistry
- 68
- Total
- 204
RahulMaths 97 · Bengaluru
- CardNo
- 11
- Name
- Rahul
- Gender
- M
- DateOfBirth
- 30 Apr
- CityTown
- Bengaluru
- Mathematics
- 97
- Physics
- 92
- Chemistry
- 92
- Total
- 281
SrinidhiMaths 52 · Chennai
- CardNo
- 12
- Name
- Srinidhi
- Gender
- F
- DateOfBirth
- 14 Jan
- CityTown
- Chennai
- Mathematics
- 52
- Physics
- 64
- Chemistry
- 71
- Total
- 187
GopiMaths 65 · Madurai
- CardNo
- 13
- Name
- Gopi
- Gender
- M
- DateOfBirth
- 6 May
- CityTown
- Madurai
- Mathematics
- 65
- Physics
- 73
- Chemistry
- 89
- Total
- 227
SophiaMaths 89 · Trichy
- CardNo
- 14
- Name
- Sophia
- Gender
- F
- DateOfBirth
- 23 July
- CityTown
- Trichy
- Mathematics
- 89
- Physics
- 62
- Chemistry
- 93
- Total
- 244
GoutamiMaths 76 · Theni
- CardNo
- 15
- Name
- Goutami
- Gender
- F
- DateOfBirth
- 22 Sep
- CityTown
- Theni
- Mathematics
- 76
- Physics
- 58
- Chemistry
- 90
- Total
- 224
TauseefMaths 87 · Trichy
- CardNo
- 16
- Name
- Tauseef
- Gender
- M
- DateOfBirth
- 30 Dec
- CityTown
- Trichy
- Mathematics
- 87
- Physics
- 86
- Chemistry
- 43
- Total
- 216
ArshadMaths 62 · Chennai
- CardNo
- 17
- Name
- Arshad
- Gender
- M
- DateOfBirth
- 14 Dec
- CityTown
- Chennai
- Mathematics
- 62
- Physics
- 81
- Chemistry
- 67
- Total
- 210
AbiramiMaths 72 · Erode
- CardNo
- 18
- Name
- Abirami
- Gender
- F
- DateOfBirth
- 9 Oct
- CityTown
- Erode
- Mathematics
- 72
- Physics
- 92
- Chemistry
- 97
- Total
- 261
VetrivelMaths 56 · Trichy
- CardNo
- 19
- Name
- Vetrivel
- Gender
- M
- DateOfBirth
- 30 Aug
- CityTown
- Trichy
- Mathematics
- 56
- Physics
- 78
- Chemistry
- 62
- Total
- 196
KalyanMaths 93 · Vellore
- CardNo
- 20
- Name
- Kalyan
- Gender
- M
- DateOfBirth
- 17 Sep
- CityTown
- Vellore
- Mathematics
- 93
- Physics
- 68
- Chemistry
- 91
- Total
- 252
MonikaMaths 78 · Bengaluru
- CardNo
- 21
- Name
- Monika
- Gender
- F
- DateOfBirth
- 15 Mar
- CityTown
- Bengaluru
- Mathematics
- 78
- Physics
- 69
- Chemistry
- 74
- Total
- 221
PriyaMaths 62 · Nagercoil
- CardNo
- 22
- Name
- Priya
- Gender
- F
- DateOfBirth
- 17 Jul
- CityTown
- Nagercoil
- Mathematics
- 62
- Physics
- 62
- Chemistry
- 57
- Total
- 181
DeepikaMaths 97 · Bengaluru
- CardNo
- 23
- Name
- Deepika
- Gender
- F
- DateOfBirth
- 13 May
- CityTown
- Bengaluru
- Mathematics
- 97
- Physics
- 91
- Chemistry
- 88
- Total
- 276
SiddharthMaths 44 · Madurai
- CardNo
- 24
- Name
- Siddharth
- Gender
- M
- DateOfBirth
- 26 Dec
- CityTown
- Madurai
- Mathematics
- 44
- Physics
- 72
- Chemistry
- 58
- Total
- 174
GeetaMaths 87 · Chennai
- CardNo
- 25
- Name
- Geeta
- Gender
- F
- DateOfBirth
- 16 May
- CityTown
- Chennai
- Mathematics
- 87
- Physics
- 75
- Chemistry
- 92
- Total
- 254
JKMaths 74 · Chennai
- CardNo
- 26
- Name
- JK
- Gender
- M
- DateOfBirth
- 22 Jul
- CityTown
- Chennai
- Mathematics
- 74
- Physics
- 71
- Chemistry
- 82
- Total
- 227
JaganMaths 81 · Madurai
- CardNo
- 27
- Name
- Jagan
- Gender
- M
- DateOfBirth
- 4 Mar
- CityTown
- Madurai
- Mathematics
- 81
- Physics
- 76
- Chemistry
- 52
- Total
- 209
NishaMaths 74 · Madurai
- CardNo
- 28
- Name
- Nisha
- Gender
- F
- DateOfBirth
- 10 Sep
- CityTown
- Madurai
- Mathematics
- 74
- Physics
- 83
- Chemistry
- 83
- Total
- 240
NaveenMaths 72 · Vellore
- CardNo
- 29
- Name
- Naveen
- Gender
- M
- DateOfBirth
- 13 Oct
- CityTown
- Vellore
- Mathematics
- 72
- Physics
- 66
- Chemistry
- 81
- Total
- 219
Sequence number, marks and count
| Subtype | Allowed values in the exercise | Meaningful use |
|---|---|---|
| SeqNo | Integers from 0 to a chosen Max | Identify a card; compare identity or position when specified. |
| Marks | Integers 0–100 for one subject | Compare scores or build an appropriately typed total. |
| Count | 0,1,2,…, possibly limited by dataset size | Count cases; add compatible counts and compare. |
| TMarks | 0–300 for three whole-number subject scores | Store one student’s combined three-subject total. |
Max = 10,000 is a possible design choice from the lecture, not a universal limit on computers or datasets. If identifiers begin at zero, define the maximum ID and the number of available IDs carefully.
Storage arithmetic is not always meaningful domain arithmetic
Adding two student IDs does not create a meaningful student ID. The lecture restricts operations on Marks and Count for its examples; those are domain choices, not claims that multiplication or division of numbers is always meaningless. For example, sum divided by count gives an average, with a suitable numerical result type.
An operation may leave the subtype’s range
If Marks permits only 0–100, then 80+70 = 150 cannot be stored as a single-subject Mark. Use a larger TotalMarks or accumulator type. Similarly, subtracting count 7 from count 3 gives −4, which is an integer difference but not a nonnegative Count. Check result types and ranges, not only the operands.
Character and string subtypes
| Subtype | Exercise restriction |
|---|---|
| Gender/group label | The lecture dataset uses characters M or F. |
| Names | Alphabetic text under the simplified slide rule. |
| City | Alphabetic text under the simplified slide rule. |
| Words | The dataset allows letters/numerals and specified punctuation. |
| Category | A permitted part-of-speech label, such as Noun, Verb or Adjective. |
These are rules for the teaching datasets. Real names and city names can legitimately contain spaces, punctuation or other writing systems, and real datasets may use different gender categories. Design the allowed values from the actual application rather than declaring the classroom simplifications universal.
Equality still needs a clear meaning
For literal string equality, both strings must have the same length and the same character at each position. “Chennai” and “chennai” differ under a case-sensitive rule. Standardizing case or spaces may help category matching, but it does not automatically establish that two people have the same identity.
Try it yourself
Can Count store −2 if its definition allows only 0,1,2,…?
Show explained answer
No. A difference can be negative, but its result then needs a suitable integer type rather than Count.
Try it yourself
Three subject marks are 80,70,90. Which subtype suits their total?
Show explained answer
The total is 240, so use TMarks or another total type allowing up to 300, not single-subject Marks limited to 100.
Try it yourself
A SeqNo permits 0–10000. Is 10001 valid?
Show explained answer
No. It exceeds the chosen maximum, even though it is a valid integer.
Try it yourself
Should real names be rejected solely because the classroom Name subtype disallows punctuation?
Show explained answer
No. The exercise rule is a simplified contract. Real applications need rules that fit valid names in their intended population.
Source: Lecture 1.8 — Subtypes of basic datatypes. Small teaching datasets and diagrams are prepared for these notes; lecture and tutorial totals are identified explicitly.