Aispre 2 Finals - Lesson 1 & 2 - System Design - Database Concepts

**AISPrE 2:(Finals)** **LESSON 1:** **System Design** **[SYSTEM DESIGN]** - is the [phase that bridges the gap] between problem domain and the existing system in a manageable way. **[TYPES OF SYSTEM DESIGN:]** - **Logical Design -** [pertains to an abstract] representation of the data flo...

**AISPrE 2:(Finals)** **LESSON 1:** **System Design** **[SYSTEM DESIGN]** - is the [phase that bridges the gap] between problem domain and the existing system in a manageable way. **[TYPES OF SYSTEM DESIGN:]** - **Logical Design -** [pertains to an abstract] representation of the data flow, inputs, and outputs of the system. - **Physical Design - [ ]**[It relates to the actual input and output] processes of the system. It focuses on how data is entered into a system, verified, processed, and displayed as output. - **Architectural Design -** It is also known as high level design that focuses on the design of system architecture. It [describes the structure and behavior of the system]. It defines the structure and relationship between various modules of system development process. - **Detailed Design - [ ]**[It follows Architectural design] and focuses on development of each module. **[Conceptual Data Modeling]** \- It is representation of organizational data which includes all the major entities and relationship. **[Entity Relationship Model (E-R model)]** \- It is a technique used in database design that helps describe the relationship between various entities of an organization. **[Terms used in E-R model:]** **ENTITY** − It [specifies distinct real world] items in an application. For example: vendor, item, student, course, teachers, etc. **RELATIONSHIP** - They are the [meaningful dependencies] between entities. For example, vendor supplies items, teacher teaches courses, then supplies and course are relationship. **ATTRIBUTES** - It [specifies the properties] of relationships. ***Symbols used in E-R model and their respective meanings:***  **LESSON 2:** **System Design** **[File Organization]** -It describes how records are stored within a file. ***There are four file organization methods:*** 1. **SERIAL** - Records are stored in chronological order. 2. **SEQUENTIAL** - Records are stored in order based on a key field which contains a value that uniquely identifies a record. 3. **DIRECT (RELATIVE)** - Each record is stored based on a physical address or location on the device. ***[Address]*** is calculated from the value stored in the record's key field. 4. **INDEXED** - Records can be processed both sequentially and non-sequentially using indexes. **[File Access] -** methods allow computer programs read or write records in a file. **[Sequential Access] -** It is efficient when a large number of the records on the file need to be accessed at any given time. **[Direct (Random) Access] -**Records are located by knowing their physical locations or addresses on the device rather than their positions relative to other records. ***Types of Files used in an Organization System*** - **MASTER FILE** − It contains the current information for a system. - **TABLE FILE** - It is a type of master file that changes infrequently and stored in a tabular format. - **TRANSACTION FILE** - It contains the day-to-day information generated from business activities. - **TEMPORARY FILE** - It is created and used whenever needed by a system. - **MIRROR FILE** - They are the exact duplicates of other files. - **LOG FILES** - They contain copies of master and transaction records in order to chronicle any changes that are made to the master file. - **ARCHIVE FILES** - Backup files that contain historical versions of other files. **[DOCUMENTATION CONTROL]** **Documentation** - is a process of recording the information for any reference or operational purpose. **[Programmers or Systems Analysts]** \- usually are responsible for preparing documentation to help users learn the system. **LESSON 3:** **System Design** **[Four Main Types of Documentations:]** - - - - **[Program Documentation]** It describes inputs, outputs, and processing logic for all the program modules. The program documentation process starts in the system analysis phase and continues during implementation. This documentation guides programmers, who construct modules that are well supported by internal and external comments and descriptions that can be understood and maintained easily. **[Operations Documentation]** It contains all the information needed for processing and distributing online and printed output. Operations documentation should be clear, concise, and available online if possible. **[User Documentation]** is valuable in training users and for reference purpose. It must be clear, understandable, and readily accessible to users at all levels. **[System Documentation]** serves as the technical specifications for the IS and how the objectives of the IS are accomplished. provides the basis for understanding the technical aspects of the IS when modifications are made. **LESSON 4:** **Design Strategies** **[TOP-DOWN STRATEGY]** \- uses the modular approach to develop the design of a system. It starts from the top or the highest-level module and moves towards the lowest level modules. **[BOTTOM-UP STRATEGY]** \- It follows the modular approach to develop the design of the system. It starts from the bottom or the basic level modules and moves towards the highest level modules. **LESSON 5:** **Design Strategies** **[STRUCTURED DESIGN]** -It is a data-flow based methodology that helps in identifying the input and output of the developing system. \- The **main objective** of structured design is *[to minimize the complexity and increase the modularity of a program. ]* **[MODULARIZATION]** \- Structured design partitions the program into small and independent modules. \- Modularization or decomposition *[to minimize the complexity and to manage the problem by subdividing it into smaller segments.]* **[STRUCTURED CHARTS]** \- They are a [recommended tool] for designing a modular, top down systems which define the various modules of system development and the relationship between each module. \- It [consists of diagram] consisting of rectangular boxes that represent the modules, connecting arrows, or lines. **CONTROL MODULE** - It is a higher-level module that directs lower-level modules, called [subordinate modules.] **LIBRARY MODULE** - It is a [reusable module] and [can be invoked from more than one point in the chart.] ***two different approaches to design a*** ***structured chart:*** **[Transform-Centered Structured Charts]** \- They are used when all the transactions follow same path. **[Transaction-Centered Structured Charts]** - They are used when all the transactions do not follow the same path. **[COUPLING]** \- is the [measure of the independence] of components. It defines the degree of dependency of each module of system development on the other. **[COUPLING MEASURES:]** - **CONTENT COUPLING** - [When one component actually modifies another,] then the modified component is completely dependent on modifying one. - **COMMON COUPLING** - When amount of coupling is reduced somewhat by organizing system design so that data [are accessible from a common data store.] - **CONTROL COUPLING** - When one [component passes parameters] to control the activity of another component. - **STAMP COUPLING** - [When data structures is used to pass information] from one component to another. - **DATA COUPLING** - [When only data is passed] [then components] are [connected by this coupling.] **COHESION** \- is the measure of closeness of the relationship between its components. It defines the amount of dependency of the components of a module on one another. The **[best modules]** are those that are functionally **cohesive.** The **[worst modules]** are those that are **coincidentally cohesive**. ***[The Worst Degree of Cohesion:]*** - **Coincidental cohesion** - is found in a component whose parts are [unrelated to another.] - **LOGICAL COHESION** - It is [where several logically related functions] or data elements are placed in same component. - **TEMPORAL COHESION** - is used to [initialize a system or set variables] performs several functions in sequence, but the functions are [related by timing] involved. **PROCEDURALLY COHESION** - It [is when] [functions are grouped together] in a component just to ensure this order. **SEQUENTIAL COHESION** - It is when the output from one part of a component i[s the] [input to the next part of it.] **LESSON 6:** **Input/Output and** **Forms Design** **INPUT DESIGN** \- input is the raw data that is processed to produce output. ***[Well designed input forms and screens have following properties:]*** It should serve specific purpose effectively such as storing, recording, and retrieving the information. It ensures proper completion with accuracy. It should be easy to fill and straightforward. It should focus on user's attention, consistency, and simplicity. All these objectives are obtained using the knowledge of basic design principles regarding:  ***[The objectives of input design are:]*** To design data entry procedures and to reduce input volume To design source documents for data capture or devise other data capture methods To design input data records, data entry screens, user interface screens, etc. To use validation checks and develop effective input controls. **[DATA INPUT METHODS]** \- It is important to design appropriate data input methods to prevent errors while entering data. **[INPUT INTEGRITY CONTROLS]** \- It includes a number of methods to eliminate common input errors by end-users. **[OUTPUT DESIGN]** \- During output design, developers identify the type of outputs needed, and consider the necessary output controls and prototype report layouts. **[EXTERNAL OUTPUTS]** \- enable the system to leave the trigger actions on the part of their recipients or confirm actions to their recipients. **[INTERNAL OUTPUTS]** \- are present inside the system, and used by end-users and managers. They support the management in decision making and reporting. ***Three types of reports:*** **DETAILED REPORTS** - They [contain present information] which has almost no filtering or restriction generated to assist management planning and control. **SUMMARY REPORTS** - They [contain trends and potential problems] which are categorized and summarized that are generated for managers who do not want details. **EXCEPTION REPORTS** - They c[ontain exceptions, filtered data] to some condition or standard before presenting it to the manager, as information. **[OUTPUT INTEGRITY CONTROLS]** \- include routing codes to identify the receiving system, and verification messages to confirm successful receipt of messages handled by network protocol. **Printed or screen-format reports** - should include a date/time for report printing and the data. **Multipage reports** - contain report title or description, and pagination. **Pre-printed forms** - usually include a version number and effective date. **[FORMS DESIGN]** \- Both forms and reports are the product of input and output design and are business document consisting of specified data. **[Forms] -** provide fields for data input **[Reports] -** are purely used for reading. **[OBJECTIVES OF GOOD FORM DESIGN]** A good form design is necessary to ensure the following: To keep the screen simple by giving proper sequence, information, and clear captions. To meet the intended purpose by using appropriate forms. To ensure the completion of form with accuracy. To keep the forms attractive by using icons, inverse video, or blinking cursors etc. and to facilitate navigation. **TYPES OF FORMS:** - **Flat Forms** - It is [a single copy form] prepared manually or by a machine and printed on a paper.It is a [simplest and inexpensive form] to design,print, and reproduce, which uses less volume. - **Unit Set/Snap Out Forms -** These are papers with [one-time carbons] interleaved into unit sets for either [handwritten or machine use.] - **Continuous Strip/Fanfold Forms -**These [are multiple unit forms] joined in a continuous strip with perforations between each pair of forms. It is a [less expensive] method for large volume use. - **No Carbon Required (NCR) Paper -** They use [carbon less papers] which have two chemical coatings (capsules), one on the face and the other on the back of a sheet of paper.