ESTABLISHING DATA CONTROL

Providing the controls that assure accuracy and validity of data as it passes through the system is also an essential part of systems design. Control of input to the system is usually the mos t critical, since it is during this phase that data is transferred fl'om one media to another through human action. Methods of controlling data within the computer room are more or less standard, as the intent is merely to guarantee the correctness of procedures and data output. Since fewer natural journals are produced as byproducts of direct access data processing, systems design must take into consideration the need for creating sufficient journals for auditing purposes.

Input Control and Val idation

The primary purpose of input control is to assure that every transaction presented to the sys tem is a valid one and that it is entered correctly. Once data has been entered incorrectly, recovery becomes difficult because of the speed with which it is propagated throughout the system.

Controls that aid in assuring the correctness of input include:

1. Prenumbered source documents

2. Hash totals developed at the point of origin and carried through as far as possible in the system

3. Batch totals

4. Cross-checking of manual operations

S. Automatic production of the data through the use of devices such as time clocks, counters, etc.

The use of a verifier is extremely important in obtaining accurate recording of input data from the keypunch operation. Transposition of numbers, for example, a frequent human error, can be cau gh t by the verifier.

Validity checking of data enterin g the system is accomplished in a number of ways. For example, limit checks - resulting in computer rejection of any data whose value exceeds predetermined limits - is useful in many types of applications. "Reasonableness" checks are a further possibility. The advantage of using the computer for this type of checking is the speed with which the tests are performed and the certainty that it will test every item.

Internal Control

Two types of control are standard once the data has been recorded and entered into the sys tern: (1) Operational control to assure correct run sequence and data en try, and (2) the control required to assure the accuracy of the data itself.

Label Checking

Since data on a magnetic tape or disc is not visible, files must be labeled to identify con-tent, date produced, etc. External labeling alone, however, does not always provide

absolute identification of the filE' 's con tent. To guard against the possibility of an externally mislabeled file, or the inadvertent selection of the wrong file, the same labeling information is included in the first data block of each file. This allows the computer itself to make certain it's using the correct disc or tape reel.

Label checking subroutines are incorporated in all tape and disc handling software for the UNIVAC 9200/9300 Disc System, and are performed automatically unless the programmer specifies otherwise.

Item Counts

For systems including magnetic tape, item counting is a conventional device used to ensure that individual transactions are not lost during data manipulation. Transactions are counted as they are written to a magnetic tape reel, the total count being entered on the reel's final record. When the reel is subsequently used as input to another run, the transactions are again counted and the new total previously entered in the reel's final record.

Checklists

Checkoff lists of incoming and outgoing data, used in conjunction with batch proof totals, provide assurance that all data is accounted for. The use of batch totals alone as a validation procedure guarantees only that the particular batch being processed has not lost or gained any items during prior manipulations. It does not detect the loss of an entire batch - an added security that the checklist provides.

Control Totals

Control totals, althou gh they are incorpora ted at input and retained through output, are used principally to detect the inadvertent loss or gain of items during processing. However, their use can be extended to include the detection of incorrect data within an item. For example, if the quantity of a particular item in which the quantity f~eld is accumulated for a group total is destroyed or change.d in prior processing, the control total of the individual field will reflect a data error. Other fields, however, will reflect correct dollar value control totals and the incorrect item can be isolated through the use of the individual field total.

The efficient use of con trol totals depends in part upon the determination of an optimum batch size. Too large a batch makes item searching difficult. At the same time, too small a batch requires excessive control handling because of th,e larger number of batches involved.

Output Control

The data process in g cen ter should maintain a con tinuing record of report dis tribu tion. To verify report results, such records should include dates and totals.

Error control is another consideration. Control must be established to guarantee that all errors listed and turned over to accoun ting personnel for correction are reentered in the system prior to the completion of the processing cycle. This can be accomplished by total-ing each batch of errors for cross-checktotal-ing with correction entries.

Aud iting Cons iderations

With manual or punched card data processing systems, transactions are normally recorded frequently during processing, producing an automatic audit trail in much the same way as posting to a ledger produces a day- by- day journal of transactions. With direct access systems, however, fewer natural journals such as these are produced as run byproducts.

Also, since, updated record fields are written over the old data, there is no permanent record on disc of pas t transactions.

In order to determine the accuracy with which transactions are processed, it is necessary for the system designer to devisE~ a means of tracing all the transactions which took place during a month's processing period. One such device is called a "change" journal, which can be produced, for example, as the byproduct of a maintenance run. As the main-tenance run is made, changes to the file are recorded on a magnetic tape or printed journal to serve as a record of the transactions which took place. Transactions can then be traced at a later date through a study of the journals produced.

Another method is the creation 0:: a special test deck containing as many different trans-action types as can be identified. These transtrans-actions are then fed through the processing cycle singly, and in various combinations, against a copy of the fil~s to determine the effect that each type and each combination of types has on the system.

4. PROGRAMMING

INTRODUCTION

After the complete system is charted, duplication elimina ted, records des igned, con troIs and auditing trails established, the job of programming can begin. Section 4 stresses the importance to program development of careful planning and common sense. Although this section describes a variety of programming practices directed at producing effective and error-free programs, it is not intended to be a programming text. It augments, but in no way replaces, the programmer's own knowledge and ability. The reference manuals listed in Section 3 of this document are the primary sources of programming information for the 9200/9300 Disc System.

It is recognized that the size of the staff and the scope of the programming effort will vary widely among UNIVAC 9200/9300 Disc System users. In some installations, the programming staff will be responsible for writing and testing programs. In other installa-tions, programmers may have systems design and operational responsibilities in addition to programming assignments. In either case, the need for established policy and procedures cannot be overstated.

PLANNING FOR PROGRAMMING