Medium Level Design Guidance
Decomposing The Model
Decomposition Guidelines: Rule of Thumb to Shoot For
A system needs to comprise of more than one system element. Otherwise, the distinction between system and system element would not make any since. The upper bound is any number. To facilitate understanding of the system, the architect should consider an upper bound of 7+/-2". This relates to the capacity of humans in processing data. If an architect designs the system based on this rule, he/she may face fewer difficulties explaining the system to the stakeholders. -(Model Based Systems Architecture, pg25)
Decomposition Guidelines: Balance Specificity vs Complexity
"The system architecture may depend on a number of principles regarding its organization, the and the system's evolution. The lower bound of multiplicity of each principle is zero to indicate that development can occur with no predefined principles. The upper bound of multiplicity is not further limited. A big number will not necessarily result in better architecture but increase the difficulty to find a valid solution. Principles can be rated as learning from earlier projects. Eliding principles increase the risk of additional effort for redesign in later life cycle stages of the system. " (Model Based Systems Architecture, pg26)
Functional Element Decomposition
"To make the selected elements self - consistent and representative, three criteria may be used to ensure that each element is neither trivially simple nor inordinately complex and has wide application:
1. Significance. Each functional element must perform a distinct and significant function, typically involving several elementary functions.
2. Singularity. Each functional element should fall largely within the technical scope of a single engineering discipline.
3. Commonality. The function performed by each element can be found in a wide variety of system types."
-(Systems Engineering Principles and Practice, pg46)
Common Ways to Break Your System Into Classes
Types of Interfaces
Types of Interfaces
Interfaces: "three perspectives on connectivity: logical connectivity, physical connectivity, and behavioral connectivity. "
Logical: "As we sit at our workstation writing an email, we are notionally thinking that there is some connection between us and our recipient, as depicted in the figure below. We don’t need to know a lot about networking technology to know that the e-mail will get there. This is the essence of a logical connection."
Physical: "Meanwhile, back at our workstation, we know that our computer is connected to a local network, either hard-wired or via Wi-Fi. And, we know that ultimately there is a telecommunication network that routes our email to our recipient’s local network. This chain is depicted below. These connections, while still abstracted to a certain level, represent physical connectors that help us realize a logical connection. "
Behavioral: "The third perspective considers the functionality of the software that sends and receives the message. The multipoint message exchange shows how a single instance of a “multicast message” is generated and transmitted by producer software to the network, and how software in the network generates a “replicated message” and routes to each of the three consumers. In the behavioral perspective, you can see that the message itself acts as the “connecting” element of the design."
Lastly, the three perspective are all related. The logical connection is implemented with one or more physical connections, the physical connections transport our message, and the message is generated and routed by the functionality inherent in the software. " -Mark Simons
Media Types Through An Element
Media Types Flowing Through An Element
The three basic entities that constitute media on which systems operate are "information", "material", and "energy". It is convenient to further subdivide "information" into two classes: (1) elements dealing with propagating information (radio signals), to be referred to as signal elements, and (2) those dealing with stationary information (computer programs), to be referred to as data elements.
The Four Classes of System Functional Elements
1. Signal Elements, which sense and communicate information
2. Data Elements, which interpret, organize, and manipulate information
3. Material Elements, which provide structure and transformation of materials
4. Energy Elements, which provide energy and motive power.
Note: When doing a System of Systems ibd, there will be a 5th category, activity (such as the user steering the car)
-Systems Engineering Principles and Practice pg46
Components Classes
Components Classes
• electronic
• electro - optical
• electromechanical
• mechanical
• thermomechanical
• software
-Systems Engineering Principles and Practice pg49
