SYSTEMS ANALYSIS PERSPECTIVES Thomas I. M. Ho Purdue University Computer Sciences Department and School, of Management West Lafayette, Indiana 47907 March 1976 CSD TR 182
SYSTEMS ANALYSIS
PERSPECTIVES
T h o m a s I. M . Ho Purdue University Computer Sciences Department and S c h o o l of M a n a g e m e n t West Lafayette* Indiana 47907
ABSTRACT S y s t e m s a n a l y s i s Is s o r e l y in need of a c o n c e p t u a l f r a m e w o r k that e s t a b l i s h e s p r i n c i p l e s a n d g u i d e l i n e s for t h e t a s k of t r a r s l a t i n g the qualitative a n d u n s t r u c t u r e d p e r c e o t i o n of o r g a n i z a t i o n a l i n f o r m a t i o n r e q u i r e m e n t s into t h e t e c h n i c a l a n d rigid solutions available with computerized hardware and software. T h i s p a p e r o u t l i n e s the m a j o r c h a r a c t e r i s t i c s o f a m o d e l for e r e c t i n g a b r i d g e b e t w e e n the diverse organization and computer systems that must be joined by an Information system. Structured programming has provided the p r o g r a m m e r w i t h s u c h a rrodel. S u r e l y * the s y s t e m s a n a l y s t can b e n e f i t f r o m new and o l d p e r s p e c t i v e s o n h i s e v e n m o r s c o n o l s x t i s k . INTROGUCTION It is w i d e l y r e c o g n i z e d t h a t the systems analyst's task is a formidable o n e . To p e r f o r m h i s d u t i e s * the s y s t e m s a n a l y s t m u s t r e l y u p o n a b r o a d a r r a y of d i s c i p l i n e s . In p a r t i c u l a r * he m u s t be f a m i l i a r with the i n t r i c a c i e s of two d i v e r s e w o r l d s : t h a t of t h e o r g a n i z a t i o n a n d t h a t of t h e c o m p u t e r . A s i d e from t h e o b v i o u s s i z e and complexity of t h e s e c o n c e r n s * t h e c o n t r a s t b e t w e e n t h e s e two e n d s of the s c e c t r u m is m o s t s t r i k i n g . O n o n e h a n d * t h e o r g a n i z a t i o n is q u a l i t a t i v e and unstructured. On t h e o t h e r h a n d * the c o m p u t e r is t e c h n i c a l and r i g i d . T h e r e f o r e * it Is no s u r p r i s e to a n y o n e t h a t we have had difficulty with the application of computing technology to the i n f o r m a t i o n s y s t e m s of o r g a n i z a t i o n s . T h e r e f o r e * it is c l e a r t h a t t h e d i v e r s i t y cf t h e s e d i s c i p l i n e s is the primary obstacle to the development of systems analysis. F u r t h e r m o r e * we have not orovided the systems analyst with the conceptual devices to enable him to translate an unstructured organizational Information problem into the rigid hardware and software solutions available with comouting technology. N o t e v e n the technological software solutions offered by high-level programming l a n g u a g e s a n d d a t a b a s e m a n a g e m e n t s y s t e m s h a v e c o m p l e t e l y b r i d g e d the gap between the computerized Implementation and an organization's perception of Its information system. Technological solutiors only 1
a i d t h e i m p l e m e n t a t i o n of s o l u t i o n s t h a t h a v e a l r e a d y b e e n f o r m u l a t e d . The systems analyst needs a framework to h e l p him to i n f e r the e l e m e n t s of t h e t e c h n o l o g i c a l s o l u t i o n from t h e p r o b l e m t h a t reauires the solution. Such a f r a m e w o r k w o u l d p r o v i d e t h e i n t e r f a c e n e e d e d to t r a n s l a t e the organization perspective into the computerized perspective. Achieving this interface first dictates a c h a r a c t e r i z a t i o n of the f e a t u r e s of t h e s e o o p o s i n g p e r s p e c t i v e s t h a t m u s t be l i n k e d together. THE SYSTEMS
PERSPECTIVE
The unifying perspective on or g e n i z a t i o r s a n d c o m p u t e r s is the systems perspective. T h e p e r c e p t i o n of t h e s e e n t i t i e s a s systems is an Indispensable aid to u n d e r s t a n d i n g their respective essential features. T h e o r g a n i z a t i o n s y s t e m is c o m p o s e d of f u n c t i o n a l s u b s y s t e m s that represent the v a r i o u s f u n c t i o n s p e r f o r m e d by t h e o r g a n i z a t i o n . Each of t h e s e s u b s y s t e m s p e r f o r m s a c t i o n s or d e c i s i o r s in o r d e r to achieve designated g o a l s . T h e s e a c t i o n s or d e c i s i o n s c a n o n l y be m a d e if the s u b s y s t e m r e c e i v e s the data that establishes the constraints and o b j e c t i v e s of t h e d e c i s i o n . For e x a m p l e * t h e p r o d u c t i o n s u b s y s t e m h a s responsibility for decision-making relevant to the manufacturing function* e . g . w h a t to m a k e * h o w m a n y to m a k e * a n d w h e n to m a k e t h e m . T h e s e d e c i s i o n s c a n be m a d e o n l y If d a t a Is a v a i l a b l e on the demand for products and on the a v a i l a b i l i t y of r e s o u r c e s for p r o d u c t i o n . T h i s d a t a is only available from the environment and from other subsystems. For example* the m a r k e t i n g s u b s y s t e m p r o v i d e s d a t a on p r o d u c t demand end the inventory subsystem provides data on raw material availability. T h e p r o d u c t i o n floor e n v i r o n m e n t p r o v i d e s data o n t h e a v a i l a b i l i t y of m a n p o w e r a n d m a c h i n e r y . This interaction among subsystems requires the establishment of interfaces between the s u b s y s t e m s to .enable t h e m to f u n c t i o n In an integrated fashion to a c c o m p l i s h their r e s p e c t i v e g o a l s . The computer system is c o m p o s e d of f u n c t i o n a l s u b s y s t e m s t h a t r e p r e s e n t the v a r i o u s f u n c t i o n s p e r f o r m e d b y the computer. Each of these subsystems fulfills its d e s i g n a t e d r o l e in the p e r f o r m a n c e of computer workloads. A subsystem can fulfill its rote only If it Interacts with the other s u b s y s t e m s t h a t s u p p o r t its f u n c t i o n . In t h i s way* t h e i n p u t s u b s y s t e m r e c e i v e s the d a t a to be p r o c e s s e d * the storage subsystem stores t h e d a t a b e f o r e and a f t e r it Is p r o c e s s e d * t h e p r o c e s s i n g s u b s y s t e m p r o c e s s e s the d a t a * a n d the o u t p u t subsystem generates the data after processing. This interaction ationg s u b s y s t e m s a l s o r e a u l r e s t h e e s t a b l i s h m e n t of i n t e r f a c e s between the subsystems to enable them to f u n c t i o n in a n i n t e g r a t e d f a s M o n t o p r o c e s s the w o r k l o a d . 2
(
Finally* the systems perspective offers the concent of a decoupling mechanism to e n a b l e I n t e r f a c i n g s u b s y s t e m s to I n t e r a c t in orderly fashion. Therefore* organizations maintain inventories to compensate for unequal rates of raw material procurement and consumption. An inventory is a decoupling mechanism between the purchasing and production subsystems. C o m p u t e r s u s e s t a n d a r d data r e p r e s e n t a t i o n s to e n a b l e t h e i r f u n c t i o n a l s u b s y s t e m s to communicate w i t h each o t h e r . The organization system a n d the c o m p u t e r s y s t e m a r e thetrselves i n t e r a c t i ng subsystems of an overall system. Therefore* these subsystems possess an interface that requires a d e c o u o l i n g m e c h a n i s m to s i m p l i f y their Interaction. This decoupling mechanism is an information system model. This m o d e l p r o v i d e s a s t a n d a r d t h a t e n a b l e s o r g a n i z a t i o n s y s t e m c o n c e p t s to b e e x p r e s s e d in a c o n c e p t u a l f r a m e w o r k t h a t is a l s o c o m p a t i b l e w i t h c o m p u t e r s y s t e m c o n c e o t s . PROPERTIES
OF AN
INFORMATION S Y S T E M MODEL i The information system model is interacting subsystems:
itself
a system comoosed
of
1. Input subsystem 2. Output subsystem 3. Data base subsystem Process subsystem. T h e c o r r e s p o n d e n c e to the v a r i o u s s u b s y s t e m s of the c o m p u t e r s y s t e m is clear and t h i s is no s u r p r i s e . C o r r e s p o n d e n c e to t h e e l e m e n t s of the o r g a n i z a t i o n a l s u b s y s t e m can b e established. The elements of the output s u b s y s t e m c o r r e s p o n d to t h e a p t i o n s and d e c i s i o n s p e r f o r m e d b y e a c h o r g a n i z a t i o n s u b s y s t e m . T h e e l e m e n t s of the process subsystem c o r r e s p o n d to t h e p r o c e d u r e s a n d m o d e l s u s e d to p e r f o r m e a c h a c t i o n or d e c i s i o n . T h e e l e m e n t s of the i n p u t s u b s y s t e m c o r r e s p o n d to the data r e c e i v e d f r o m t h e e n v i r o n m e n t b y t h e e l e m e n t s of the p r o c e s s s u b s y s t e m to g e n e r a t e the elements of the output subsystem. Finally* the elements of the d a t a b a s e s u b s y s t e m c o r r e s c o n d to the d a t a r e c e i v e d from another process by an element of the process subsystem to generate the elements of t h e o u t p u t s u b s y s t e m . For e x a m p l e * in t h e c a s e of t h e p r o d u c t i o n s u b s y s t e m * t h e e l e m e n t s of its o u t p u t s u b s y s t e m conpose t h e p r o d u c t i o n s c h e d u l e t h a t a s s i g n s m a n o o w e r * m a c h i n e r y * and m a t e r i a l r e s o u r c e s to the m a n u f a c t u r i n g f u n c t i o n . The e l e m e n t s of the process subsystem compose the production scheduling model. The e l e m e n t s of the I n p u t s u b s y s t e m c o m p o s e the t r a n s a c t i o n s that report tha status of m a n p o w e r a n d m a c h i n e r y r e s o u r c e s . The e l e m e n t s of the d a t a base s u b s y s t e m c o m p o s e the data that r e n o r t product demand and r a w m a t e r i a l a v a i l a b i l i t y from t h e s a t e s f o r e c a s t a n d I n v e n t o r y s t a t u s e l e m e n t s of t h e p r o c e s s s u b s y s t e m .
3
T h e d a t a b a s e s u b s y s t e m s e r v e s as s d e c o u p l i n g m e c h a n i s m between the Input and o u t p u t s u b s y s t e m s . T h e i n p u t s u b s y s t e m g a t h e r s t h e data from the e n v i r o n m e n t to be u s e d to generate information to the environment through the output subsystem. However* the output s u b s y s t e m d o e s n o t n e c e s s a r i l y g e n e r a t e I n f o r m a t i o n a t the same time n o r a t the s a m e r a t e a s t h e i n p u t s u b s y s t e m r e c e i v e s d a t a . Therefore* the data base subsystem is an inventory of data resources. Furthermore* the output subsystem does not necessarily request i n f o r m a t i o n In a f o r m a t t h a t is i d e n t i c a l w i t h t h a t of t h e data used to generate t h e d e s i r e d i n f o r m a t i o n . H e n c e * t h e data b a s e s u b s y s t e m m a i n t a i n s a s t a n d a r d s p e c i f i c a t i o n for data resources In order to decouple the incompatibilities between the input and output subsystems. T h e d e c o u p l i n g r o l e of t h e d a t a b a s e s u b s y s t e m In these respects motivates the residence of the d a t a b a s e s u b s y s t e m in the s t o r a g e s u b s y s t e m of a c o m p u t e r s y s t e m . W i t h r e s p e c t to the o r g a n i z a t i o n s y s t e m * t h e d a t a b a s e subsystem also functions as a decoupling m e c h a n i s m . The v a r i o u s functional s u b s y s t e m s of a n o r g a n i z a t i o n s y s t e m a r e i n t e r a c t i n g subsystems that must communicate w i t h o n e a n o t h e r to a c h i e v e t h e d e s i r e d s y n e r g i s t i c e f f e c t . Again* the data base s u b s y s t e m s e r v e s as both an inventory and as a standard for the d a t a r e s o u r c e s t h a t a r e g e n e r a t e d b y a n y f u n c t i o n a l s u b s y s t e m a n d c a n be u s e d b y a n y o t h e r f u n c t i o n a l s u b s y s t e m in p u r s u i t of t h a t s u b s y s t e m ' s o b j e c t i v e s . Similarly* the data base s u b s y s t e m also d e c o u p l e s separate procedures and models within a single subsystem. H o w e v e r * it is t h e d a t a b a s e s u b s y s t e m ' s r o l e a s a d e c o u p l i n g m e c h a n i s m b e t w e e n f u n c t i o n a l s u b s y s t e m s that e l e v a t e s it to Its c e n t r a l r o l e in an i n t e g r a t e d i n f o r m a t i o n s y s t e m . In order to f u n c t i o n e f f e c t i v e l y a s a d e c o u p l i n g m e c h a n i s m * the d a t e b a s e s u b s y s t e m m u s t m a i n t a i n the data resources so that they accurately r e f l e c t the s t a t e of t h e o r g a n i z a t i o n a l e n v i r o n m e n t . Only in t h i s way c a n t h e p r o c e s s s u b s y s t e m u s e t h e data r e s o u r c e s to e f f e c t the appropriate organizational decisions and a c t i o n s . T h e r e f o r e * the p r o c e s s s u b s y s t e m f u n c t i o n s as a data base control mechanism that insures that the data base subsystem maintains the standard e s t a b l i s h e d by t h e e n v i r o n m e n t . Then* the update function of the process subsystem senses the s t a t e of t h e d a t a b a s e for c o m p a r i s o n w i t h t h e s t a t e of t h e environment. [f the data base is n o t in conformance* the update function invokes a f e e d b a c k m e c h a n i s m to m o d i f y the d a t a b a s e to c o n f o r m to the s t a t e of the e n v i r o n m e n t . T h e a p p l i c a t i o n of t h i s s y s t e m s c o n c e p t u a l f r a m e w o r k to systeis analysis requires a means to d e s c r i b e t h e e l e m e n t s of the v a r i o u s s u b s y s t e m s in o r d e r t o p e r c e i v e t h e i r r e l e v a n t characteristics. The r e s u l t i n g d e s c r i p t i o n is a b l u e p r i n t for the d e s i g n of the i n f o r m a t i o n s y s t e m w h o s e r e q u i r e m e n t s a r e d e t e r m i n e d b y the s y s t e m s a r a l y s i s . The blueprint is an implementation of the concepts m o t i v a t e d b y the information system model. The model identifies the essential characteristics of t h e e l e m e n t s of the m o d e l ' s s u b s y s t e m s in o r d e r to 4
describe computer system.
t h o s e p r o o e r t i e s that a r e r e l e v a n t to the orqanizaticn and systems that must be united by the desired i n f o r m a t i o n
An e l e m e n t of a s u b s y s t e m is c a l l e d a r e l a t i o n a l s t r u c t u r e * a set of data n a m e s . A re I a t IonaI s t r u c t u r e is s i m p l y a f i r s t n o r m a l form r e l a t i o n as defined by Codd III. The collection of relational structures that compose a subsystem represent a template of p e r m i s s i b l e f o r m s that may be assumed by data residing i r that subsystem. Data moves from o n e s u b s y s t e m to a n o t h e r a t p r e s c r i b e d r a t e s and a c c o r d i n g to p r e s c r i b e d r u l e s . T h e r e l e v a n t c h a r a c t e r i s t i c s of a r e l a t i o n a l s t r u c t u r e i n c l u d e : 1. Composition 2. I d e n t If Icat i o n 3 . T i m i ng t. Volume. Composition describes the data n a m e s t h a t c o m p o s e a r e l a t i o n a l structure. Composition defines various types of relational structures. T h e d i s t i n c t i o n b e t w e e n a r e l a t i o n a l s t r u c t u r e t y o e and a r e l a t i o n a l s t r u c t u r e o c c u r r e n c e is c r u c i a l . T h e type represents the composition of the structure. Tha o c c u r r e n c e r e p r e s e n t s a n i n s t a n c e of t h e s t r u c t u r e . An o c c u r r e n c e c o r r e s p o n d s to s o m e i d e n t i t y in the real w o r l d t h a t is b e i n g r e p r e s e n t e d b y t h e o c c u r r e n c e . For e x a m p l e * t h e r e l a t i o n a l s t r u c t u r e t y p e T I M E - C A R D = {EMPL-NCJ* PAY-PERIOD* H9SWORKED> represents a n i n p u t t r a n s a c t i o n for r e p o r t i n g e m p l o y e e tlire. The occurrence set OClTIME-CARD) = foe f T I M E - C A R D * 1 1 : 1 * i < !OC(TIME-CARDI•> represents all possible transactions far all e m p l o y e e s a n d all p a y p e r i o d s . T o d i s t i n g u i s h one o c c u r r e n c e of a relational structure from other occurrences of t h e s a m e r e l a t i o n a l s t r u c t u r e * o n e or m o r e data n a m e s of the s t r u c t u r e a r e d e s i g n a t e d a s i d e n t i f i e r s . T h e i d e n t i f i e r s form an identifier set* a subset of t h e c o r r e s p o n d i n g r e l a t i o n a l s t r u c t u r e * so t h a t t h e i d e n t i f i e r set o c c u r r e n c e of an occurrence of the structure is n o t I d e n t i c a l to t h e i d e n t i f i e r set o c c u r r e n c e s of all other o c c u r r e n c e s . T h e c o n c e p t of i d e n t i f i c a t i o n is e s s e n t i a l to the operation of matching corresponding occurrences of d i f f e r e n t r e l a t i o n a l s t r u c t u r e s to e n a b l e t h e flow of a data item from one relational s t r u c t u r e to a n o t h e r . T h e s p e c i f i c a t i o n of t h i s d a t a flow f r o m one i n f o r m a t i o n s y s t e m m o d e l s u b s y s t e m to a n o t h e r Is the purpose o f t h e I n f o r m a t i o n s y s t e m b l u e p r i n t t h a t w ^ s e e k to c o n s t r u c t . This d a t a flow o c c u r s at p r e s c r i b e d r a t e s t h a t a r e d e t e r m i n e d b y the timing and volume of the various relational structures. The timing of a r e l a t i o n a l s t r u c t u r e I n d i c a t e s t h e f r e a u e n c y of d a t a flow Into the s u b s y s t e m in w h i c h the s t r u c t u r e r e s i d e s . Together with the frequency* the v o l u m e of a r e l a t i o n a l s t r u c t u r e d i c t a t e s the r a t e of d a t a flow into the s u b s y s t e m in w h i c h t h e s t r u c t u r e r e s i d e s . 5
ADVANTAGES
DF AN
INFORMATION SYSTEM
MODEL
T h e a d v a n t a g e s of t h i s m a t h e m a t i c a l f o r m u l a t i o n of a n i n f o r m a t i o n system are m a n i f o l d . U s i n g m a t h e m a t i c s a s a v e h i c l e for d e s c r i p t i o n of the m o d e I a f f o r d s t h e c l a r i t y of e x p r e s s i o n for which mathematics Is recognized. T h i s a p p r o a c h is c o n s i s t e n t w i t h the e a r l i e r e f f o r t s of Y o u n g a n d K e n t 121 a n d the C O D A S Y L D e v e l o p m e n t Committee 13 1 . A c o m p r e h e n s i v e f o r m a l d e f i n i t i o n of the m o d e l d e s c r i b e d h e r e i n h a s b e e n p r e s e n t e d by H o a n d N u n a m a k e r 1 4 1 . T h a t formulation also motivates another a d v a n t a g e of thB m a t h e m a t i c a l a p p r o a c h . T h e m o d e l is u s e d as t h e f o u n d a t i o n for d e t e r m i n a t i o n of the q u a l i t y of a s y s t e m s a n a l y s i s . Precise definitions of r e q u i r e m e n t s c o m p l e t e n e s s and c o n s i s t e n c y lay t h e f o u n d a t i o n for e s t a b l i s h i n g p r i n c i p l e s a n d G u i d e l i n e s for systems analysis. The absence of s u c h p r i n c i p l e s is the m a j o r c a u s e of the c u r r e n t incomplete and i n c o n s i s t e n t system studies uoon which many system design efforts have relied. T h i s s i t u a t i o n h a s r e s u l t e d in a m u l t i t u d e of i n f o r m a t i o n s y s t e m f a i l u r e s for w h i c h Morgan and Soden (51 p r o v i d e a g l i m o s e a t o n l y a v e r y s m a l l s a m p l e . Aside from the much-needed introduction of riqor into the p r a c t i c e of s y s t e m s a n a l y s i s * t h e e s t a b l i s h me nt of a forir^l approach t o s y s t e m s a n a l y s i s c r e a t e s the o v e r d u e o p p o r t u n i t y for d e v e l o p m e n t of t o o l s for t h e m a n a g e m e n t of systems analysis. Armed with only a motley assortment of g r a p h i c a l and n a r r a t i v e d e v i c e s for d e s c r i b i n g n u m e r o u s c o m p l e x s y s t e m r e q u i r e m e n t s * t o d a y ' s s y s t e m s a n a l y s t is f a c e d with an u n e n v i a b l e task. However* the situation is no longer d e s p e r a t e s i n c e t h e a d v e n t of c o m p u t e r - a i d e d t e c h n i q u e s to a s s i s t the systems analyst. Most notable a m o n g t h e s e t e c h n i q u e s h a s b e e n the development of Requirements Statement Languages. A Requirements Statement Language ( R S L ) is a h i g h - l e v e l l a n g u a g e for use by s y s t e m s a n a l y s t s in d e s c r i b i n g t h e r e q u i r e m e n t s of information systems. An RSt Is n o t a programming language since a requirements statement expresses what organizational requirements an information system fulfills rather than how those requirements a r e i m o l e m e n t e d in a h a r d w a r e and software solution. In other words* a requirements statement is a n application of the f o r m a l I n f o r m a t i o n s y s t e m model that interfaces the o r g a n i z a t i o n and c o m p u t e r s y s t e m s . The effective use of Requirements Statement Languages is s u p p o r t e d by s o f t w a r e p a c k a g e s k n o w n as R e q u i r e m e n t s S t a t e m e n t A n a l y z e r s (RSA) that m a i n t a i n requirements s t a t e m e n t s for s u b s e a u e n t u s e by all s y s t e m s d e v e l o p m e n t personnel. The maintenance of a requirements statement uses RSA algorithms that perform logical checks on RSL statements for c o m p l i a n c e w i t h t h e c o m p l e t e n e s s a n d c o n s i s t e n c y p r o p e r t i e s d e f i n e d in terms of t h e I n f o r m a t i o n s y s t e m m o d a l . F i n a l l y * an R S A a l s o d i s p l a y s t h e s y s t e m r e q u i r e m e n t s in v a r i o u s t a b u l a r a n d s r a o h i c a l f o r m a t s that enable the communication of system requirements to all p e r s o n n e l I n v o l v e d in t h e s y s t e m s d e v e l o p m e n t e f f o r t . T h e m o s t a d v a n c e d i m p l e m e n t a t i o n of the R S L / R S A a p p r o a c h is the Problem Statement L a n g u a g e / P r o b I em Statement Analy/.er (PSL/PSAl ft
d e v e l o p e d by t h e I n f o r m a t i o n S y s t e m s D e s i g n and Optimization System (ISDOS) Project [61. PSL is an E n g l i s h - l i k e language p o s s e s s i n g flexible facilities for< d e s c r i b i n g data definition* timing* and volume. However* PSL facilities for describing s y s t e m flOH only p r o v i d e t h e c a p a b i l i t y to d o c u m e n t h i g h - l e v e l f l o w w i t h o u t Indicating data manipulation and processing requirements at the data element level. PSA provides extensive capabIlities for maintaining and displaying system requirements expressed in a PSL statement. T h e r e f o r e * P S L and PSA p r o v i d e s u p e r i o r f a c i l i t i e s for managing the d o c u m e n t a t i o n of h i g h - l e v e l s y s t e m r e q u i r e m e n t s . The Accurately Defined Systems ( A D S ) t e c h n i q u e 171 p r o v i d e s a p r a c t i c a l m e t h o d for d o c u m e n t i n g system flow at the data element level. ADS d e s c r i b e s t h e m e m b e r s of the o u t p u t * input* p r o c e s s * and data base subsystems by Indicating the data e l e m e n t s that c o m p o s e the relational structures in e a c h s u b s y s t e m . Then* ADS d o c u m e n t s s y s t e m f l o w by I n d i c a t i n g the s o u r c e of each d a t a e l e m e n t o c c u r r e n c e in each r e l a t i o n a l s t r u c t u r e of t h e o u t p u t * p r o c e s s * a n d data b a s e s u b s y s t e m s . A s o u r c e Is a n o t h e r d a t a e l e m e n t o c c u r r e n c e in a r e l a t i o n a l structure of e i t h e r t h e input* p r o c e s s * or d a t a b a s e s u b s y s t e m . T h e u s e of ADS a s an RSL is v i t a l l y a i d e d by a n R S A f o r A D S reported by Nunamaker* Ho» Konsynski* and Singer ( 8 1 . M o s t I m p o r t a n t of all* b o t h PSL and A D S a n d t h e i r a c c o m p a n y i n g s o f t w a r e a r e c u r r e n t l y b e i n g u s e d in a c t u a l s y s t e m s d e v e l o p m e n t and in s y s t e m s a n a l y s i s t r a i n i n g . T h e m o s t i m p o r t a n t a d v a n c e in s u p p o r t of the P S L / R S A a n p r o a c h has b e e n t h e d e v e l o p m e n t of s o f t w a r e for a i d i n g p r o g r a m module and data base design In fulfillment of the r e q u i r e m e n t s e x p r e s s e d in a n RSL statement. S o f t w a r e for t h e g e n e r a t i o n of a data b a s e s c h e m a and of data management a o p l i c a t i on programs f r o m a PSL s t a t e m e n t h a s b e e n d e v e l o p e d by B l o s s e r 1 9 1 . S o f t w a r e for t h e g e n e r a t i o n of orogramming s p e c i f i c a t i o n s f r o m an ADS s t a t e m e n t h a s b e e n d e v e l o p e d by Ho [ 1 0 1 . CONCLUSION The future of s y s t e m s a n a l y s i s is b r i g h t e n e d by the p r o s p e c t of t h e g e n e r a l a v a i l a b i l i t y of a d v a n c e d tools and techniques for the performance and management of this d i f f i c u l t t a s k . A l t h o u g h t h e s e t o o l s are n o t y e t g e n e r a l l y a v a i l a b l e * today's systems analyst can a l r e a d y b e n e f i t f r o m the I n s i g h t s Into t h e a n a l y s i s f u n c t i o n t h a t h a v e b o o n g a i n e d f r o m t h e f o r m u l a t i o n of m o d e l s u p o n w h i c h the tools are based. The systems analyst can take advantage of a conceptual f r a m e w o r k to g u i d e his analysis in m u c h the same way that the p r o g r a m m e r is g u i d e d by t h e m a x i m s of s t r u c t u r e d p r o g r a m m i n g .
7
REFERENCES
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1 . Codd* E. F . 1970. A relational m o d e l of d a t a for large s h a r e d d a t a b a n k s . Cqdkb-.-A£H 13* 6 ( J u n e 1970)* 3 7 7 - 3 8 7 . 2 . Young* J . W . J r . and Kent* H . K* 1 9 5 8 . Abstract formulation of data processing problems. d Q u t Q a L _ Q l _ l Q d u s t L i a l _ E a a i Q a a c i . Q o (Nov.D e c . 1958)* 4 7 1 - 4 7 9 . 3 . C O D A S Y L D e v e I o p m e n t C ommi t t e e . 1 9 6 2 . An i n f o r m a t i o n a l g e b r a o h a s e 1 r e p o r t . Cooo—ACti 5* 4 (April 1962)* 1 9 0 - 2 0 4 . 4 . Ho* Thomas I. M. and N u n a m a k e r * J . F . J r . 1974. Requirements s t a t e m e n t l a n g u a g e p r i n c i p l e s for a u t o m a t i c o r o g r a m m l n g . £lqc.___19Z4 iCfl-Uatiocal-QoDiataDca (Nov. 1974)* 2 7 9 - 2 8 8 . 5- M o r g a n * H . L . a n d Soden* J . V . 1 9 7 3 . U n d e r s t a n d i n g fIS f a i l u r e s . D a t a - B a s e 5* 2-4 ( W i n t e r 19731* 1 5 7 - 1 6 7 . 6 . T e l c h r o e w * D . a n d Sayani* H . 1 9 7 1 . A u t o m a t i o n of s y s t e m b u i l d i n g . O a t a a a l i o a 17* 16 ( A u g u s t 15* 1 9 7 1 ) * 2 5 - 3 0 . 7 . Lynch* H . J. 1969. ADS= a technique in s y s t e m d o c u m e n t a t i o n . D a l a - B a s a 1* 1 (Spring 1969)* 6 - 1 8 . 8 . N u n a m a k e r * J . F . Jr.; Ho* T . ; K o n s y n s k l * B.; a n d S i n g e r * C . 1976. Co«puter~a I ded a n a l y s i s of i n f o r m a t i o n s y s t e m s . C.oas._&CU* to a p p e a r during Spring* 1976. 9 . B l o s s e r * P . A . 1 9 7 6 . An a u t o m a t i c s y s t e m for a p p l i c a t i o n s o f t w a r e g e n e r a t i o n a n d p o r t a b i l i t y . P h . D . d i s s e r t a t i o n * P u r d u e U n i v e r s i t y (in progress). 1 0 . Ho* T. 1974. Toward a formal theory for the requirements statement* analysis* and design of information systems. Ph.D. dissertation* Purdue University (December 1 9 7 4 ) .