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Entity Relationship Diagrams explained using the Emergency Medical Hologram's medical database (from Star Trek:Voyager) as an example.
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Prescription
Prescription
Prescription
Dr. Lewis Zimmerman459
Patient name: Tom Paris
Stardate: 41153.7
Drug: Tri-Ox Compound
Take twice a day
Dr. Lewis Zimmerman459
Patient name: Tom Paris
Stardate: 41153.7
Drug: Tri-Ox Compound
Take twice a day
Prescription
Dr. Lewis Zimmerman459
Patient name: Tom Paris
Stardate: 41153.7
Drug: Tri-Ox Compound
Take twice a day
Doctor
Patient
Date
Drug
Frequency
Prescriptionnumber
Dr. Lewis Zimmerman459
Patient name: Tom Paris
Stardate: 41153.7
Drug: Tri-Ox Compound
Take twice a day
PrescriptionPrescriptionIDDoctorNamePatientNameDrugName
DateFrequency
PrescriptionPrescriptionIDDoctorNamePatientNameDrugName
DateFrequency
Prescription
ID
Doctor
Name
Patient
Name
Drug
Name Date
Frequency
(per day)
1Dr. Lewis
Zimmerman
Tom
Paris Tri-Ox
42231.2
2
2Dr. Julian
Bashir
Odo Hyronalin 45432.1
3
3Lewis
Zimmerman
Harry
Kim
Tri-Ox 42235.2
7
4Dr. Beverly
Crusher
Lt. Data Hyronalin 45912.3
1
5Dr. Bashir Odo Synaptizine 48796.6
2
6L.
ZimmermanTom
Paris
Priaxate 42765.5
90
7Dr. Lewis
Zimmerman
Tom
Paris
Tri-Ox 42604.4
5
8Dr. L.
Zimmerman
Katherine
Janeway
Hyronalin 45673.4
4
9Dr.
Phlox
T’Pol Tri-Ox 37389.5
3
• Two Problems:– Lots of text repeated over and over (e.g.
“Tri-Ox”, “Tom Paris”) and imagine this for tens of thousands of records, it really eats up computation power
– Slightly different ways of referring to the same thing (e.g. “Dr. Lewis Zimmerman”, “Dr. L. Zimmerman”, “Lewis Zimmerman”)
• Solution:– Create a number of tables that lists all of
the text fields and assigns them a number
• So:– Create a Doctor
Table that lists all of the Doctors and assigns them a number
Doctor
ID
Doctor
Name
1 Dr. Lewis
Zimmerman
2 Dr. Julian
Bashir
3 Dr. Beverly
Crusher
4 Dr.
Phlox
Prescription
ID
Doctor
Name
Patient
Name
Drug
Name Date
Frequency
(per day)
1Dr. Lewis
Zimmerman
Tom
Paris Tri-Ox
42231.2
2
2Dr. Julian
Bashir
Odo Hyronalin 45432.1
3
3Lewis
Zimmerman
Harry
Kim
Tri-Ox 42235.2
7
4Dr. Beverly
Crusher
Lt. Data Hyronalin 45912.3
1
5Dr. Bashir Odo Synaptizine 48796.6
2
6L.
ZimmermanTom
Paris
Priaxate 42765.5
90
7Dr. Lewis
Zimmerman
Tom
Paris
Tri-Ox 42604.4
5
8Dr. L.
Zimmerman
Katherine
Janeway
Hyronalin 45673.4
4
9Dr.
Phlox
T’Pol Tri-Ox 37389.5
3
Prescription
ID
Doctor
ID
Patient
Name
Drug
Name Date
Frequency
(per day)
1 1 Tom
Paris Tri-Ox
42231.2
2
2 2 Odo Hyronalin 45432.1
3
3 1 Harry
Kim
Tri-Ox 42235.2
7
4 2 Lt. Data Hyronalin 45912.3
1
5 2 Odo Synaptizine 48796.6
2
6 1 Tom
Paris
Priaxate 42765.5
90
7 1 Tom
Paris
Tri-Ox 42604.4
5
8 1 Katherine
Janeway
Hyronalin 45673.4
4
9 4 T’Pol Tri-Ox 37389.5
3
• So:– Now create a
Patient Table that lists all of the patients and assigns them a number
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Prescription
ID
Doctor
ID
Patient
Name
Drug
Name Date
Frequency
(per day)
1 1 Tom
Paris Tri-Ox
42231.2
2
2 2 Odo Hyronalin 45432.1
3
3 1 Harry
Kim
Tri-Ox 42235.2
7
4 2 Lt. Data Hyronalin 45912.3
1
5 2 Odo Synaptizine 48796.6
2
6 1 Tom
Paris
Priaxate 42765.5
90
7 1 Tom
Paris
Tri-Ox 42604.4
5
8 1 Katherine
Janeway
Hyronalin 45673.4
4
9 4 T’Pol Tri-Ox 37389.5
3
Prescription
ID
Doctor
ID
Patient
ID
Drug
Name Date
Frequency
(per day)
1 1 1 Tri-Ox
42231.2
2
2 2 2 Hyronalin 45432.1
3
3 1 3 Tri-Ox 42235.2
7
4 2 4 Hyronalin 45912.3
1
5 2 2 Synaptizine 48796.6
2
6 1 1 Priaxate 42765.5
90
7 1 1 Tri-Ox 42604.4
5
8 1 5 Hyronalin 45673.4
4
9 4 6 Tri-Ox 37389.5
3
• So:– Now create a
Drug Table that lists all of the drugs and assigns them a number
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Doctor
ID
Patient
ID
Drug
Name Date
Frequency
(per day)
1 1 1 Tri-Ox
42231.2
2
2 2 2 Hyronalin 45432.1
3
3 1 3 Tri-Ox 42235.2
7
4 2 4 Hyronalin 45912.3
1
5 2 2 Synaptizine 48796.6
2
6 1 1 Priaxate 42765.5
90
7 1 1 Tri-Ox 42604.4
5
8 1 5 Hyronalin 45673.4
4
9 4 6 Tri-Ox 37389.5
3
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2
2
2 2 2 2 45432.1
3
3 1 3 1 42235.2
7
4 2 4 2 45912.3
1
5 2 2 3 48796.6
2
6 1 1 4 42765.5
90
7 1 1 1 42604.4
5
8 1 5 2 45673.4
4
9 4 6 1 37389.5
3
• So what we’ve ended up with is…
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
• Note:– Now all of the values in the Prescription
Table are numbers, this is great because the computer will be much faster at processing prescriptions (because it loves dealing with numbers), which is good since the Prescription Table will be added to most frequently.
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
• Also:– If a drug name is changed, e.g. “Tri-Ox” to
“Tricordrazine”, then you only need to change it once and it is done for all of the prescriptions. And this eliminates the possibility of some being changed and some not, since the DrugName now only occurs in one place in the whole database.
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
• Compare this with the original design where we would have to change every occurrence of the drug name.
Prescription
ID
Doctor
Name
Patient
Name
Drug
Name Date
Frequency
(per day)
1Dr. Lewis
Zimmerman
Tom
Paris Tri-Ox
42231.2
2
2Dr. Julian
Bashir
Odo Hyronalin 45432.1
3
3Lewis
Zimmerman
Harry
Kim
Tri-Ox 42235.2
7
4Dr. Beverly
Crusher
Lt. Data Hyronalin 45912.3
1
5Dr. Bashir Odo Synaptizine 48796.6
2
6L.
ZimmermanTom
Paris
Priaxate 42765.5
90
7Dr. Lewis
Zimmerman
Tom
Paris
Tri-Ox 42604.4
5
8Dr. L.
Zimmerman
Katherine
Janeway
Hyronalin 45673.4
4
9Dr.
Phlox
T’Pol Tri-Ox 37389.5
3
Prescription
ID
Doctor
Name
Patient
Name
Drug
Name Date
Frequency
(per day)
1Dr. Lewis
Zimmerman
Tom
Paris Tri-Ox
42231.2
2
2Dr. Julian
Bashir
Odo Hyronalin 45432.1
3
3Lewis
Zimmerman
Harry
Kim
Tri-Ox 42235.2
7
4Dr. Beverly
Crusher
Lt. Data Hyronalin 45912.3
1
5Dr. Bashir Odo Synaptizine 48796.6
2
6L.
ZimmermanTom
Paris
Priaxate 42765.5
90
7Dr. Lewis
Zimmerman
Tom
Paris
Tri-Ox 42604.4
5
8Dr. L.
Zimmerman
Katherine
Janeway
Hyronalin 45673.4
4
9Dr.
Phlox
T’Pol Tri-Ox 37389.5
3
• And what if we forgot to change of them ???
Prescription
ID
Doctor
Name
Patient
Name
Drug
Name Date
Frequency
(per day)
1Dr. Lewis
Zimmerman
Tom
Paris Tri-Ox
42231.2
2
2Dr. Julian
Bashir
Odo Hyronalin 45432.1
3
3Lewis
Zimmerman
Harry
Kim
Tri-Ox 42235.2
7
4Dr. Beverly
Crusher
Lt. Data Hyronalin 45912.3
1
5Dr. Bashir Odo Synaptizine 48796.6
2
6L.
ZimmermanTom
Paris
Priaxate 42765.5
90
7Dr. Lewis
Zimmerman
Tom
Paris
Tri-Ox 42604.4
5
8Dr. L.
Zimmerman
Katherine
Janeway
Hyronalin 45673.4
4
9Dr.
Phlox
T’Pol Tri-Ox 37389.5
3
• Ooops
• that’s going to cause problems, the integrity of the data is compromised.
• So it’s better to separate things out into individual tables.
Prescription
ID
Doctor
ID
Patient
ID
Drug
ID Date
Frequency
(per day)
1 1 1 1 42231.2 2
2 2 2 2 45432.1 3
3 1 3 1 42235.2 7
4 2 4 2 45912.3 1
5 2 2 3 48796.6 2
6 1 1 4 42765.5 90
7 1 1 1 42604.4 5
8 1 5 2 45673.4 4
9 4 6 1 37389.5 3
Drug
ID
Drug
Name
1 Tri-Ox
2 Hyronalin
3 Synaptizine
4 Priaxate
Prescription
ID
Patient
Name
1 Tom
Paris
2 Odo
3 Harry
Kim
4 Lt. Data
5 Katherine
Janeway
6 T’Pol
Doctor
ID
Doctor
Name
1 Dr. Lewis Zimmerman
2 Dr. Julian Bashir
3 Dr. Beverly Crusher
4 Dr. Phlox
PrescriptionID
DoctorID
PatientID
DrugID
Date
Frequency
Prescription
Insertnew
prescriptionrecord
Prescription
Insertnew
prescriptionrecord
Drug
Check if the drug on the prescriptionis a real and existing drug
Prescription
Drug
Insertnew
prescriptionrecord
Patient
Check if the patient on the prescriptionis a real and existing patient
Prescription
Drug
Insertnew
prescriptionrecord
Patient
Check if the doctor on the Prescription
is a real and existing doctor
Doctor
Prescription
Drug
Patient
Doctor
Prescription
Drug
Patient
Doctor
Prescription
Drug
Patient
Doctor
PrescriptionIDDoctorIDPatientIDDrugID
DateFrequency
DrugIDDrugName
RecommendedDosageSide-Effects
PatientIDPatientName
PatientAddressSympthomsOccupation
DoctorIDDoctorName
Qualifications
Prescription
Drug
Patient
Doctor
PrescriptionIDDoctorIDPatientIDDrugID
DateFrequency
DrugIDDrugName
RecommendedDosageSide-Effects
DoctorIDDoctorName
Qualifications
PatientIDPatientName
PatientAddressSympthomsOccupation
