CSE1301 Computer Programming:

Lecture 28Transaction Processing

Topics

• Dataflow Diagrams

• Data structures (structs, arrays)

• Transaction Processing Example – Dataflow Diagram– Structs as parameters

• Reading: Brookshear, 6.4

Structure chart with labels showing data coupling

inviteToParty ( name , date , venue ){ ringUp ( name ) askToParty (date , venue ) sayGoodbye ( name )}

askToParty sayGoodbyeringUp

inviteToParty

name

date

venue

namename

date

venue

control coupling

data coupling

Recall:

Dataflow Diagrams (DFD)

• Pictorial representation of data paths:

– origin (source)

– destination (sink, storage)

– processing points (location of data manipulation, modules)

Dataflow diagram showing data paths

inviteToParty

Mom

Ad

dre

ss B

oo

k

date & venue

name

Invitatio

n List

ringUp

name

phone

Friendgreeting

askToParty

date & venue

date & venue

sayGoodbye

name

salu

tatio

n

Friend

sayGoodbye

ringUp

inviteToParty

askToParty

Mom

Ad

dre

ss B

oo

k

date & venue

name

Invitatio

n List

name

phone

greeting

date & venue

date & venue

name

salu

tatio

n

Arrows: Data Paths

Friend

sayGoodbye

ringUp

inviteToParty

askToParty

Mom

Ad

dre

ss B

oo

k

date & venue

name

Invitatio

n List

name

phone

greeting

date & venue

date & venue

name

salu

tatio

n

Boxes: Data Sources and Sinks

Friend

sayGoodbye

ringUp

inviteToParty

askToParty

Mom

Ad

dre

ss B

oo

k

date & venue

name

Invitatio

n List

name

phone

greeting

date & venue

date & venue

name

salu

tatio

n

Circles (Bubbles): Processing Points

Friend

sayGoodbye

ringUp

inviteToParty

askToParty

Mom

Ad

dre

ss B

oo

k

date & venue

name

Invitatio

n List

name

phone

greeting

date & venue

date & venue

name

salu

tatio

n

Heavy Straight Lines: Data Storage

Friend

sayGoodbye

ringUp

inviteToParty

askToParty

Mom

Ad

dre

ss B

oo

k

date & venue

name

Invitatio

n List

name

phone

greeting

date & venue

date & venue

name

salu

tatio

n

Note: You are not included in the diagram!

Dataflow diagrams (DFD)

• Emphasise the data (information) to flow through system.

(rather than procedures to be executed)

• By following data paths, discover where data units merge, split, are altered.

Transaction Processing: Dataflow Diagram

• What are the actions / data manipulation?

• What are the data sources / sinks?

• What data is stored?

• Example: ATM Transaction

Example: Transactions

• Actions / Data Processing:– withdraw cash

– transfer funds

– determine balance

– deposit money (??)

– authenticate customer

Authenticate: Algorithm

read card number from ATM cardask the Customer for PIN numbersearch the Customer Database for that card numberif card number is found{ retrieve Customer’s PIN on record if PIN on record matches the PIN keyed in { return card number and PIN Okay }}

return BAD card number and PIN

Authenticate: Dataflow Diagram

Authenticate

Customer

PIN

Cu

sto

mer

Dat

abas

e

PIN on record

card number

ATM Card

card number

Transfer

Withdraw

result

& card number

resu

lt

& ca

rd n

umbe

r

Authenticate: Data

struct CustomerIDRec{ long cardNumber; int pin;};

typedef struct CustomerIDRec CustomerID;

• card number– an integer of many digits

• PIN– a 4-digit number

Withdraw: Dataflow Diagram

Withdraw

Customer

account type and amount

Cu

sto

mer

Dat

abas

e

balance

card number and account type result and

card number Authenticate

new balance

cash

Customer Record

• How would you represent a record in the customer database?

struct CustomerRec{ char name[NAMELEN]; long cardNumber; int pin; long chequeAccountNumber; float chequeAccountBalance; long savingsAccountNumber; float savingsAccountBalance;};

typedef struct CustomerRec Customer;

Customer Record

struct CustomerRec{ char name[NAMELEN]; long cardNumber; int pin; long chequeAccountNumber; float chequeAccountBalance; long savingsAccountNumber; float savingsAccountBalance;};

typedef struct CustomerRec Customer;

Already defined as: CustomerID

Customer Record

struct CustomerRec{ char name[NAMELEN]; CustomerID id; long chequeAccountNumber; float chequeAccountBalance; long savingsAccountNumber; float savingsAccountBalance;};

typedef struct CustomerRec Customer;

struct CustomerRec{ char name[NAMELEN]; CustomerID id; long chequeAccountNumber; float chequeAccountBalance; long savingsAccountNumber; float savingsAccountBalance;};

typedef struct CustomerRec Customer;

Customer RecordProblems:• Cumbersome• How do we know which ones are open?

struct CustomerRec{ char name[NAMELEN]; CustomerID id; Account accounts[2];};

typedef struct CustomerRec Customer;

Customer Recordstruct AccountRec{ int open; /* boolean */ long number; float balance;};

typedef struct AccountRec Account;

struct CustomerRec{ char name[NAMELEN]; CustomerID id; Account accounts[2];};

typedef struct CustomerRec Customer;

Customer Recordstruct AccountRec{ int open; /* boolean */ long number; float balance;};

typedef struct AccountRec Account;

Index determines account type:accounts[0]: cheque accountaccounts[1]: savings account

More scalable!

Example 1: printBalance

void printBalance ( Customer cust ){ int type;

printf(“Customer name: %s\n”, cust.name); for (type=0; type < 2; type++) { if (cust.accounts[type].open) { printf(“Account number: “); printf(“%ld\n”, cust.accounts[type].number); printf(“Balance: “); printf(“%.2f\n”, cust.accounts[type].balance); } } printf(“\n”);}

Customer Database

struct DatabaseInfo{ int count; /* Number of records. */ Customer customers[MAXRECORDS];};

typedef struct DatabaseInfo Database;

void printAllbalance ( Database db ){ int i;

for (i=0; i < db.count; i++) { printBalance ( db.customer[i] ); }}

Example 2: printAllBalance

Transaction Data

ATM BANK’SMAINFRAME

card number and request for PIN

PIN on record

card number and request for balance

balance

card number and balance update

confirmation

• Potential problems with this setup: security, link break-up, traffic.

ATM BANK’SMAINFRAME

request

response

Transaction Data

Transaction Data

struct requestRec{ int type; /* 0=balance, 1=withdraw, etc */ CustomerID id; /* card no. and PIN keyed in */ int accountFrom; /* account type */ int accountTo; /* account type */ float amount;};

typdef struct requestRec Request;

• Disadvantages: Large record, some fields unused.• Advantages: Security, processed in mainframe,

shorter response, less traffic.

Transaction Data

struct responseRec{ int code; /* 0=ok, 1=wrong pin, 2=no funds, .. */ float amount;};

typdef struct responseRec Response;

Transaction Processing

Response processRequest ( Request req ){ Response response;

if (req.type == 0) response = doBalance(req); else if (req.type == 1) response = doWithdraw(req); else if (req.type == 2) response = doTransfer(req); else

/* ...and so on... */

return (response); }

Updating StructsCustomer updateCustomer ( Customer cust ){ printf(“Customer name: %s\n, cust.name); printf(“Enter new card number: “); scanf(“%ld”, &(cust.id.cardNumber)); printf(“Enter new PIN: “); scanf(“%d”, &(cust.id.pin));

return cust;}

...

cust = updateCustomer(cust);

...

Can we avoidlong identifies?

new id

Hierarchy and Data Coupling

updateID updateAccountupdateName

updateCustomer

customer

customer

old account old name

old id

new name new account

The size of the data coupling corresponds roughly to the level of the module in the hierarchy.

Hierarchy and Data CouplingCustomer updateCustomer ( Customer cust ){ updateName ( cust.name ); cust.id = updateID ( cust.id ); cust.account[0] = updateAccount ( cust.account[0] ); cust.account[1] = updateAccount ( cust.account[1] );

return cust;}

Exercise: Dataflow diagram

Draw a dataflow diagram depicting the flow of information between a lecturer, a student, and a textbook. Include the fact that an end of semester examination is given.

• Data sources? – Lecturer, textbook

• Data storage? – Student memory, notebooks

• Data manipulation? – Read textbook, compile information, answer questions

Summary

• Dataflow diagrams are an alternative representation of a system.

• Transaction processing: focus on dataflow and data structures.

• Combination of: – top down and bottom up;– design tools and techniques.

• Readings: Brookshear. 6.4, Fig 6-6