Indirection
This refers to a design principle whereby a class is placed to act as an intermediate between two classes to disengage them while still linking them (John W. Satzinger, 2016). The principle can also be used to decouple the components of a system. With indirection, instructions do not pass straight from point X to point Y, instead, an intermediate point Z in introduced such that the instructions are passed form point X to Y through point Z. Point Z therefore becomes the central point of communication between X and Y.
This design principle is used to enforce protection from variations. It allows the variations in a single system/component to be isolated in the intermediate class or component. Indirection is used for corporate security systems such as firewalls.
The insertion of a use case controller is an example of indirection. The controller acts as a separate class that takes in all the input and channels it to the respective domain classes.
This refers to a system which has components that are shared among several people or groups in a company (GLOSSARY, n.d.). Enterprise level systems are used to satisfy the requirements and needs of an organization rather than the needs of an individual. They aim at improving the enterprises’ efficiency and productivity by providing a functionality which supports business logic implementation.
Pseudostate
This refers to the commencing point of a state machine diagram denoted by a black dot. They are primarily used to connect multiple transitions into more complex state transitions paths (State Machine Diagrams, 2017). Pseudostates entail:
Schema
This refers to a component of a database that has all the descriptive information about the data contained in the physical data store. The schema is essential because it contains data that describes the rules and structure for accessing the application domain data. A schema is made up of tables, the relations among the specific tables, details of the data items and access and content controls (John W. Satzinger, 2016).
There are three different types of schema which are defined according to the levels of abstraction of the three-level architecture. They include: External schemas, conceptual schemas and the internal schema. the external schema maps to the different views of the data, the conceptual describes the entities, attributes and relationships whereas the internal schema is a full description of the internal model.
This is a database system in which data is stored in the form of records or tuples so that relations between different attributes can be easily established and used for data access and transformation. A relational database management system provides room for recombining data elements in order to form different relation resulting in a great flexibility of data usage (Haithcoat, 2017).
The advantages of a relational database management system include: rigorous design methodology, ease of use, modifiable and fast processing, multi-user access, network access, avoids duplication of data, data is stored only once.
The disadvantages include: thorough planning is required, easy to create badly designed systems if data analysis isn’t done properly.
An implementation diagram describes the different elements that are required for system implementation. It models the high-level software components and their interfaces. It does not describe the functionality of the system but instead it describes the components used to achieve those functionalities.
A deployment diagram describes the hardware used in the system in system implementation. It is intended for visualization of elements and components that connect two device nodes and represents the communication that takes place between them. They consist of nodes and their relationships (UML – Deployment Diagrams, 2017). They are used to visualize the hardware topology of a system, describe hardware components and describe the runtime processing nodes.
Singleton design pattern is used to ensure that a class has only one instance and give and a global access point to it. It is also used to enforce the encapsulated just-in-time-initialization (sourcemaking, 2017). It solves the problem that an application needs one, and only one object instantiated.
The state chart was brought into place so that the different states of a component in a system can be recorded. State charts describe the different states of an object during its lifetime and the events that change the respective states. State charts are very useful when modelling reactive system (systems that respond to internal or external events). They outline the flow of control from one state to the next.
The state charts have the following main purposes:
Defining a state machine to model the states of an object, describing different states of an object during its lifetime, modelling the lifetime of a reactive system, and lastly, modeling the dynamic aspect of a system.
A DBMS in made up of several components and each component plays a very vital role in the DBMS environment. The components include: Software, hardware, data, procedures, and People (Connolly).
Software
This is the main component of the database management system. It is a set of programs that play a great part in managing and controlling the overall computerized database. The DBMS software is the most significant component, the OS including network software, and the application programs developed by third parties such as java, visual basic etc.
Hardware
Hardware is required in order for the DBMS and the applications to run. It consists of a set of physical devices such as storage devices, computers, I/O devices. A DBMS requires a specific amount of main memory and disk space to run.
Data
This is the most important component of the DBMS environment from the end-users point of view. It acts as a bridge between the human and machine components. Both operational and metadata are contained in the database. In addition, the data also incorporates the system catalog.
Procedures
They refer to the rules and instructions that dictate the design and use of database. The procedure on how to use the system is always documented for the users to make use of. The documented procedures may consist of instructions on how to: log onto the system, start of stop the system, make backup copies of the DBMS.
People
There are four distinct types of people who play key roles in a DBMS environment. They include: data and database administrators, database designers, application developers, and the end users.
Data and database administrators
Responsible for the management of the data resource including maintenance of standards, policies and procedures
Responsible for the physical realization of the database for instance: security and integrity control, maintenance of operational system
Database designers
There are two kinds of database designers: the logical and physical database designers. The logical designer focuses more on the data, relations between the data, and the constraints enforced on the data.
The physical designer focuses on how the logical database design is to be physically realized. This entails: mapping the logical database design into a set of tables and integrity constraints, enforcing the security measures required on the data and selecting the specific storage structures to achieve optimum performance.
Application developers
They write application programs that provide the required functionality for the end users as outlined by the systems analyst.
Specification for a pattern has the following elements: name, explanation, constituents, context of use, usability results and user feedback, and a solution.
Name
This serves as a unique identity of the pattern
Explanation
This describes where the pattern can be used
Constituents
This presents the constituent elements necessary for applying the pattern
Solution
This defines the rules that are required for transforming the requirements into formal expressions.
Context of use
The context description provides the instances/context that the specific design pattern cab be best applied.
Usability results and user feedback
This contains all the feedback received from the users concerning the specific pattern.
References
Connolly, T. (n.d.). DATABASE SYSTEMS (4 ed.). Amsterdam: Pearson Education.
GLOSSARY. (n.d.). Retrieved from https://web.ydu.edu.tw/: https://web.ydu.edu.tw/~alan9956/docu1/sa/glossary.pdf
Haithcoat, T. (2017). Relational Database Management Systems, Database Design, and GIS. Retrieved from https://msdis.missouri.edu/: https://msdis.missouri.edu/resources/gis_advanced/pdf/Relational.pdf
John W. Satzinger, R. B. (2016). Systems Analysis and Design in a Changing World (7 ed.). USA.
sourcemaking. (2017). Singleton Design Pattern. Retrieved from sourcemaking.com: https://sourcemaking.com/design_patterns/singleton
State Machine Diagrams. (2017). Retrieved from https://www.uml-diagrams.org/: https://www.uml-diagrams.org/state-machine-diagrams.html
UML – Deployment Diagrams. (2017). Retrieved from Tutorials Point: https://www.tutorialspoint.com/uml/uml_deployment_diagram.htm
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