Copyright: ©2005 by Elsevier Inc. All rights reserved. 1 Chapter - 2 Basics of Sound Structure Author: Graeme C. Simsion and Graham C. Witt

Copyright: ©2005 by Elsevier Inc. All rights reserved. 2 Drug Expenditure Survey Form

Copyright: ©2005 by Elsevier Inc. All rights reserved. 3 Notes (1) Each hospital has a unique hospital number to distinguish it from other hospitals (in some cases two hospitals had the same name) and were prefixed “H” (for “hospital”). Operation numbers were assigned sequentially by each hospital. Hospitals fell into three categories: “T” for “teaching”, “P” for “public”, and “V” for “private”. All teaching hospitals were public (“T” implied “P”).

Copyright: ©2005 by Elsevier Inc. All rights reserved. 4 Notes (2) The operation code was a standard international code for the named operation. Procedure group was a broader classification. The surgeon number was allocated by individual hospitals to allow surgeons to retain a degree of anonymity. The prefix “S” stood for “surgeon”. Only a single surgeon number was recorded for each operation. Total drug cost was the total cost of all drug doses for the operation. The bottom of the form recorded the individual antibiotic drugs used in the operation. A drug code was made up of a short name for the drug plus the size of the dose.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 5 Automated Survey Database: Initial Drug Expenditure Model OPERATION (Hospital Number, Operation Number, Hospital Name, Hospital Category, Contact Person, Operation Name, Operation Code, Procedure Group, Surgeon Number, Surgeon Specialty, Total Drug Cost, Drug Code 1, Drug Name 1, Manufacturer 1, Method of Administration 1, Dose Cost 1, Number of Doses 1, Drug Code 2, Drug Name 2, Manufacturer 2, Method of Administration 2, Dose Cost 2, Number of Doses 2, Drug Code 3, Drug Name 3, Manufacturer 3, Method of Administration 3, Dose Cost 3, Number of Doses 3, Drug Code 4, Drug Name 4, Manufacturer 4, Method of Administration 4, Dose Cost 4, Number of Doses 4)

Copyright: ©2005 by Elsevier Inc. All rights reserved. 6 Notes about the database We want to avoid redundant data (avoids errors) The database is based on tables consisting of rows and columns Each cell in the table can only contain one fact No order can be assumed in the table We need to identify each row in the table (so that we can get at each row later)

Copyright: ©2005 by Elsevier Inc. All rights reserved. 7 One Fact per Column (1) The Drug Code column holds both a short name for the drug and a dosage size, two distinct facts. –Eg. “MAX 150mg” The dosage size (150mg) in turn consists of a numeric size (150) and a unit of measure (mg). –The three facts should be recorded in separate columns.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 8 One Fact per Column (2) A more subtle example of a multi-fact column is the Hospital Category. –Public or private (first fact) and –Does the hospital provides teaching (second fact). We should establish two columns, Hospital Type and Teaching Status, to capture these distinct ideas.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 9 Hidden Data Have we lost any data in the translation to tabular form? We cannot assume that data are stored in the order entered (there is no assumed order). Sequence numbers help here. If the hospitals used red forms for emergency operations and blue forms for elective surgery, we would need to add a column to record the category if it was of interest to the database users.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 10 Derivable Data To achieve the objective of non-redundancy we should remove any data that can be derived from other data in the table –The Total Drug Cost = Total of Dose Costs multiplied by the Numbers of Doses. –Assuming we need the total, we remove Total Drug Cost noting in supporting documentation how it can be derived. –Prefixing Hospital Numbers with “H” and Surgeon Numbers with “S” adds no information to the database (because column names provide context). –Include information (such as “H” and “S”) in cases where the context is lost.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 11 Why did the form include derivable data? Occasionally, there may is a regulatory requirement to hold derivable data. In some cases, derived data is included unknowingly. Most often, it is added with the intention of improving performance. –But, performance is not our concern at the logical modeling stage. –Specifying redundant data in the physical model is one option if the physical database performance is not adequate.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 12 Determining the Primary Key We cannot automatically identify each row in the table. The primary key uniquely identifies one row of the table and is a combination of columns that achieves this. –A combination of Hospital Number and Operation Number will do the job. –If we nominate a particular hospital number and operation number, there will be at most one row with that particular combination of values. The purpose of the primary key is exactly is to enable us to refer unambiguously to a specific row of a table. –We can check this with the business experts by asking: “Could there ever be more than one form with the same combination of Hospital Number and Operation Number?”

Copyright: ©2005 by Elsevier Inc. All rights reserved. 13 Where are we now? OPERATION (Hospital Number, Operation Number, Hospital Name, Hospital Type, Teaching Status, Contact Person, Operation Name, Operation Code, Procedure Group, Surgeon Number, Surgeon Specialty, Drug Short Name 1, Drug Name 1, Manufacturer 1, Size of Dose 1, Unit of Measure 1, Method of Administration 1, Dose Cost 1, Number of Doses 1, Drug Short Name 2, Drug Name 2, Manufacturer 2, Size of Dose 2, Unit of Measure 2, Method of Administration 2, Dose Cost 2, Number of Doses 2, Drug Short Name 3, Drug Name 3, Manufacturer 3, Size of Dose 3, Unit of Measure 3, Method of Administration 3, Dose Cost 3, Number of Doses 3, Drug Short Name 4, Drug Name 4, Manufacturer 4, Size of Dose 4, Unit of Measure 4, Method of Administration 4, Dose Cost 4, Number of Doses 4)

Copyright: ©2005 by Elsevier Inc. All rights reserved. 14 Major problem: Drug administration Max. 4 drugs per operation - is this a problem? –Why four? Can more the four be administered? What ‘rule’ led to this? Could this change? –Paper-based Form allowed for extra drugs to be attached. How do we do this in the database? –We cannot use this data easily in statistics: how much money is spend on Ampicillin annually? We would need complex program logic or another table. We’ve handled drugs in this example using what is called a ‘repeating group’. These are generally bad.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 15 Recognizing Repeating Groups OPERATION (Hospital Number, Operation Number, Hospital Name, Hospital Category, Teaching Status, Contact Person, Operation Name, Operation Code, Procedure Group, Surgeon Number, Surgeon Specialty, {Drug Short Name, Drug Name, Manufacturer, Size of Dose, Unit of Measure, Method of Administration, Dose Cost, Number of Doses})

Copyright: ©2005 by Elsevier Inc. All rights reserved. 16 Are there any others? Seek information about other data on the form –Can more than one surgeon be involved in an operation? If so, the data items describing surgeons (Surgeon Number and Surgeon Specialty) would become another repeating group.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 17 Removing Repeating Groups Split the original table into multiple tables (one for the basic data and one for each repeating group) as follows: –Remove each separate set of repeating group columns to new tables so that each occurrence of the group becomes a row in its new table. –Include the key of the original table in each new table –If the sequence of occurrences within a repeating group has business significance, introduce a “Sequence” column –Name each new table. –Identify and underline the primary key of each new table

Copyright: ©2005 by Elsevier Inc. All rights reserved. 18 The Database after Removing Repeating Groups OPERATION (Hospital Number, Operation Number, Hospital Name, Hospital Type, Teaching Status, Contact Person, Operation Name, Operation Code, Procedure Group, Surgeon Number, Surgeon Specialty) DRUG ADMINISTRATION (Hospital Number, Operation Number, Drug Short Name, Size of Dose, Unit of Measure, Method of Administration, Dose Cost, Number of Doses, Drug Name, Manufacturer)

Copyright: ©2005 by Elsevier Inc. All rights reserved. 19 Determining the Primary Key of the New Table “What is the minimum combination of columns needed to uniquely identify one row (i.e., one specific administration of a drug)?” To identify the individual administration we need the Drug Short Name, the Size of Dose, Unit of Measure, and Method of Administration—a six-column primary key. To verify we ask: “Can the same drug be administered in different dosages for the one operation?” (yes) and “Can the same drug and dose be administered using different methods for the one operation?” (yes, again). The primary key of the Operation table is in the Drug Administration table so we know which operation each drug administration applies to.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 20 More Problems Of Redundancy Every row operation in hospital number 17 will contain the facts that the hospital’s name is St. Vincent’s, that Fred Fleming is the contact person, that its teaching status is T, and that its type is P. Oour criterion of non-redundancy is not being met. This has consequences: –Changing any fact about a hospital will involve updating every operation for that hospital (update anomaly) –If we were to delete the last operation for a hospital, we would also be deleting the basic details of that hospital (deletion anomaly) Fix by removing Hospital (and other examples such as this) to a separate table. Keep the key of the new table as a link (foreign key) to the Operation table.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 21 Next Version of our Database OPERATION (Hospital Number, Operation Number, Operation Name, Operation Code, Procedure Group, Surgeon Number, Surgeon Specialty) HOSPITAL (Hospital Number, Hospital Name, Hospital Type, Teaching Status, Contact Person) DRUG ADMINISTRATION (Hospital Number, Operation Number, Drug Short Name, Size of Dose, Unit of Measure, Method of Administration, Dose Cost, Number of Doses, Drug Name, Manufacturer)

Copyright: ©2005 by Elsevier Inc. All rights reserved. 22 Other Similar Cases Surgeons are given numbers in each hospital but data will be lost if the last operation in the database that Surgeon S11 has performed is deleted we lose information about S11. Operation Name and Procedure group will also be lost There seems to be rich data about specific drusg that also needs to be sorted out –Drug Short Name clearly gives Drug Name and Manufacturer –It is not clear about costings of drugs administration. We need the help of our client

Copyright: ©2005 by Elsevier Inc. All rights reserved. 23 Asking Our Client Modeler: What determines Dose Cost? Client: It depends on the drug itself and the size of the dose. Modeler: So any two doses of the same drug and same size would always cost the same? Client : Assuming, of course, they were administered by the same method; injections cost more than pills. Modeler: But wouldn’t cost vary from hospital to hospital (and operation to operation)? Client : Strictly speaking, that’s true, but it’s not what we’re interested in. We want to be able to compare prescribing practices, not how good each hospital is at negotiating discounts. So we use a standardized cost. Modeler: So maybe we could call this column “Standard Dose Cost” rather than “Dose Cost”. By the way, where does the standard cost come from?

Copyright: ©2005 by Elsevier Inc. All rights reserved. 24 The Role of Business Rules Note that if the business rules were different, the results might well be different. For example, consider the rule “We use a standardized cost.” If this did not apply, the Dose Cost would also be determined by Hospital Number as well as the other data items identified. Could it be that a surgeon has more than one speciality (in which case we would have a repeating group called Surgeon Speciality) We assume this is not the case here.

Copyright: ©2005 by Elsevier Inc. All rights reserved. 25 The Final Database Model OPERATION (Hospital Number, Operation Number, Operation Code, Surgeon Number) SURGEON (Hospital Number, Surgeon Number, Surgeon Specialty) OPERATION TYPE (Operation Code, Operation Name, Procedure Group) STANDARD DRUG DOSAGE (Drug Short Name, Size of Dose, Unit of Measure, Method of Administration, Standard Dose Cost) DRUG (Drug Short Name, Drug Name, Manufacturer) HOSPITAL (Hospital Number, Hospital Name, Hospital Type, Teaching Status, Contact Person) DRUG ADMINISTRATION (Hospital Number, Operation Number, Drug Short Name, Size of Dose, Unit of Measure, Method of Administration, Number of Doses)