Ramp-up
The personnel profile during a project’s startup transient. The entire roll-off discussion also applies here, but inversely.
Range (set theory)
The set from which a value may be selected for some given variable.
Rat Hole
A useless distraction or mental contortion not often escaped once entered. The complement of “value added” (the opposite would be “value subtracted”). This refers to place for rats to go down…not an anatomical part of the rat. Many highly respected System Engineers will insist that this entire web site is one.
Reach and Access
For the sake of this discussion, engineered systems can be considered in two categories: those that are intended for human-interactive maintenance1, and those that are not. Those that are not so intended are of no interest here. The development of those that are intended for such maintenance must consider the ability of the maintainers to... read more
Real Number
Any number that is not imaginary.
Reasoning
The act of assembling or recounting a sequence or network of facts and data1 leading to an inescapable, definitive conclusion. Ostensibly, Engineers like us “reason” our way through problems to create designs. In this context, of course, “reason” implies a certain amount of logic in our thinking, which guides what data we pay attention to... read more
Reconciliation
Two Engineers are charged with making calculations: The first adds 2+2, getting 4.1 (he’s probably loaned out to the Marketing department) The second subtracts 4 -2, getting 1.9 (most likely a nervous stress analyst) Recognizing that there should have been a closer dovetailing of the two answers, management executes one or more of the following:... read more
Recovery Plan
The plan written when a failure to hold the published schedule can no longer be denied. The objective of a recovery plan is to return to the published schedule at some milestone defined thereupon, executing in accordance with the published plan thereafter. Once a project reaches a critical mass of recovery plans1, the original schedule... read more
Regression Analysis
A statistical technique wherein data are compared to certain pre-defined geometric shapes to produce meaningful descriptive simplifications like “average” and “standard deviation”. When applied to test data, this process is sometimes called “data reduction”, where the statistics are referred to as the “reduced data”. I have observed that many of the non-cognoscenti think that regression... read more
Regulatory Customer
A type of customer having oversight for the purpose of assessing compliance with legal regulations rather than with contractual obligations. Sometimes referred to as a “regulator”, but that’s a type of clock. Contrast with Acquisition Customer and End User.
Relational Database
The process, or the result therefrom, of using formal Set Theory to determine how information and the relationships between types of data should be stored. read more.
Repair
An MRB disposition for discrepant hardware resulting in a Serial Number that is no longer compliant with the released identifying drawing. Therefore, technically constituting a unique Part Number, usually comprised of the original Part Number plus the number of the directing non-conformance. Repair can be associated with limited use. Contrast with rework. The notion of... read more
Request for Information
A solicitation for information from potential suppliers of a product or service. The responses are non-binding, so should usually be taken “with a grain of salt”. They are used, in part, to manage expectations within the procuring customer. They also notify the potential technical base of emerging interest in specific materiel or services. There are... read more
Request for Proposal
An RFP solicits formal, binding information on the cost, technical, and schedule characteristics of material or services to be procured. By definition, the procurement will be the focus of management. An RFP usually includes comprehensive draft requirements, insofar as they are known at the time of procurement. The use of “TBD” (of various types) is... read more
Request for Quote
A request for cost data from one or more potential suppliers during a procurement process. The results are usually non-binding, so should be taken “with a grain of salt”. An RFQ can also include the request for schedule data, because there is often a trade-off between cost and schedule. RFQ’s are used, in part, to... read more
Requirement
A statement of need or intent. In most cases, the statement has been formally designated by the originating authority as a criterion for selection or approval. read more.
Requirement Quality
The oft-ballyhooed notion that we so well understand in the abstract all the subtleties, variations, and contextual implications of technical requirements that we can quantitatively measure their suitability for use in communicating complex technological concepts, one requirement at a time, in a manner simple enough to be executed by those who understand neither the product,... read more
Research and Development (R&D)
An effort in which an organization or individual speculatively innovates (“research”) and/or designs practical, marketable applications (“develop”).
Research Result
A feature, discovered during research, that can be expressed as a data structure like the one shown in Table 1.
Residual Uncertainty
“Residual Uncertainty” is the uncertainty that remains after formal verification is complete: the adverse difference between the limit value of a requirement measure and the proven value at the limit of Uncertainty for that same parameter. It is distinct from other uncertainties that exist during the development process. At that adverse extreme, the requirement must still... read more
Retained Regulatory Requirements
Provisions of the Federal Aviation Regulations (FAR) for which the FAA has retained direct approval authority (that is, no AR is authorized to approve certification data). The term is applicable only in the context of Commercial Aircraft.
Review
A review is a formal inspection of developmental progress, generally for the purpose of obtaining concurrence from an Acquisition Customer that work done to date indicates that the final product is reasonably expected to suit their intended purpose. Such in-process meetings functionally serve to reduce anxiety on the part of the customer with regard to... read more
Review Item Discrepancy (RID)
An issue, found during a review (e.g., SDR, PDR, or CDR) or audit (e.g., FCA or PCA), with regard to whether or not some requirement has been met by some design or work submitted with regard to that design.
Rework
An MRB disposition for discrepant hardware resulting in a Serial Number that is compliant with the released identifying drawing. Contrast with repair, which can cause additional work for the attentive System Engineer.
Roll-off
Roll-off describes the desired shape of the personnel resource profile for a project showing how people are re-deployed as a project winds down: we want the profile to decline gradually enough for the people to be absorbed by other on-going projects, avoiding a lay-off situation. When the “roll-off” is precipitous, we have to quickly find... read more
Root Cause
A root cause is an event or circumstance which, independent of all others, is sufficient to precipitate some specific result. The term is most often used in the context of Root Cause Analysis, where the “result” is a failure under investigation. Contrast with causal factor, proximate cause, and distal cause.
Run for Score
A specific test event in which data are gathered on a UUT for explicit, formal verification of compliance with one or more requirements. This phrase is less often used with respect to verification by other methods, but is sometimes used in those other methods when referring to data gathered in support of some subsequent analysis that verifies compliance.
Scalar
Formally, an individual element of a vector space. A zero-th order array. Mostly, that isn’t very helpful. As a practical matter, a scalar is a variable that needs exactly one value to describe it. Contrast with vector.
Schedule
The network of dated, resource-loaded tasks and task precedence relationships to be ignored during execution of a project.
Science
Knowledge obtained and tested by way of the Scientific Method.
Science Project
A process(2) purporting to be of the Scientific Method, but replacing the stopping criteria with the following Guru Meditation Errors 1: The investigators get bored The investigators retire The investigators find an even more gullible sugar daddy The scam gets discovered Footnotes I once owned an original-version Commodore Amiga. I wish I still had it![↩]
Scientific Method (Engineer’s version)
An algorithm comprised of the following steps: Observe phenomenon. Formulate hypothesis. Test hypothesis. Refine hypothesis based on results. Repeat until one or more of the following stopping criteria are met (in order of priority): The results are within the utility specified by the funding application in consideration of reasonable future use1; The results are within... read more
Scrap
An MRB disposition that formally precludes a Serial Number from any operational use. Usually involves physical alteration of the discrepant item (e.g., painting, part marking or otherwise disfiguring up to and including outright destruction) that irrevocably differentiates it from items accepted as complying with the requirements of the identifying drawing. Special cases include “scrap to... read more
Segment
A first-layer partition of a system. In legacy DoD Acquisition practice, a partition to be managed by a Governmental Agent (e.g., a PEO or Government Laboratory), as opposed to one for which management authority was delegated to a contractor (e.g., a Prime). Because the management was not delegated across a contractual boundary, the associated specification... read more
Selected Item Drawing
As defined by ASME Y14.24, a Selected Item Drawing does exactly what its name says: it selects certain as-built items from a production stream, rejecting others. This drawing type is identifying because the parts meeting its acceptance criteria are no longer interchangeable with any other parts for the purposes that caused the selected item drawing... read more
Selection Criteria
A list of factors to be considered when evaluating proposals. The list almost always includes the relative importance of each criterion. It should always be included in requests for proposal, to create a level playing field among all bidders. See the exegesis on mitigating biases.
Serial Number (S/N)
A type of accession identifier indicating the order in which the manufacturing of an item is planned. Not to be confused with Line Number, Effectivity or a Configuration Item Number.
Service
In software usage, a process executing without any specific login and, therefore, available to execute commands at the behest of other processes. In the Linux world, also called a “daemon”. In the early (non-multi-tasking) days of DOS, also referred to as “fork off and die”, which immediately leads to an unfortunate recommendation made to certain... read more
Service Oriented Architecture (SOA)
A conceptual approach to software development emphasizing (+/- maximizing the use of) services (definition 1) as opposed to vertically integrated application software.
Shall (usage of)
When used in a requirement, indicative of a characteristic or (occasionally) task that is intended as mandatory. The design‘s failure to comply with such a requirement is treated as a contract breach. Contrast with shall, where practicable, should, may, and will.
Shall, where practicable (usage of)
When used in a requirement, indicative of a characteristic, feature, or (occasionally) task that is considered mandatory iff it can be implemented within the existing standard design and/or manufacturing practices of the developer. The design documentation must otherwise explain what the standard practices are with respect to the stated issue. This requirement form is now typically deprecated.... read more
Sheet size
The physical size of the paper on which documentation is printed as specified by ASME Y14.1 and (for metric) Y14.1M
Sheet-form
Any drawing that is not book-form.
Should (usage of)
Advice to the developer with regard to a characteristic which, if not met by the proffered design, must be explained away by the developer. Contrast with shall, shall, where practicable, may, and will.
Similarity
The condition in which two (or more) things share a common set of characteristics. The characteristics can be either abstract or concrete. When the characteristic is a term of an equation or logical relation, we can define similarity parameters (e.g., Reynold’s Number, Nusselt Number). When used in support of formal qualification, Similarity is a sub-type... read more
Simulation
Simulation is a type of analysis proceeding through chains of events or circumstances (that is, as a matter of cause-and-effect). The term is often used when the solution of time-domain ODE’s is required to calculate an end state, or a series of intermediate states. It can, however, be used with respect to other independent variables... read more
Singular (Matrix)
A singular matrix is one that cannot be inverted. This means that solution techniques that use division by any such matrix cannot be employed. Here, “dividing” refers to the notion that because we have (for example) Distance = Rate * Time, we can calculate rate by inverting the equation: Time = Distance / Rate. If... read more
Sketch
A preliminary type of drawing (typically Level II).
Smokescreen
A low-cost set of activities and data designed to distract the attention of people who cannot tell the difference from the poor performance of the real work not getting done per schedule. Or, occasionally, the marketing of a scheduled activity to cover for the execution of an unscheduled activity that would otherwise have made management... read more
Software
Practical, but unofficial definition: data and instructions compiled and linked, or capable of being compiled and linked, into machine readable form such that the resulting executable must be loaded into an OS-controlled memory space in order to run. (i.e., it executes in a different memory space than where it is stored).
Software Installation Drawing (SID)
An identifying drawing that configuration controls software and its installation in a production environment. A SID is often little more than a simple drawing that points to an SVD and assigns a P/N in the production system.
Software Version Description (SVD)
A document (not a drawing) that describes a particular release of software, along with the instructions for installing it and adapting it to some specific locale or usage.
Software Version Description Drawing (SVDD)
In some companies, combines the characteristics of an SVD and a SID into a single drawing type. Not currently found in ASME Y14.24.
Solicitation
A solicitation is a procurement action where information is sought by a solicitor. Types include (but are not limited to) RFI, RFQ, and RFP. A solicitor might be acting on their own behalf, or might be acting as the agent for some other entity (e.g., an Acquisition Customer).
Source Code
Human-readable software, prior to compilation.
Source Control Drawing (SCD)
A type of PCD used for the circumstance where an existing part is sufficient to our design purpose, but new qualification data1 must be paid for by the customer (which may, or may not be, the developer). See also the CI Development Cycle (Intermediate). Footnotes The new data are necessary in order to verify the item’s compliance with a wider... read more
Specification (Spec)
Generally, a collection of requirements for a CI or standard design. Certain types of specifications can, however, contain requirements for processes that are specific to some given project (or class of CI), which sometimes causes confusion with the concept of a Standard. read more.
Specification Tailoring
The practice of identifying individual requirements within a General Specification for applicability to a specific project.
Specification Tree
A dendrogram of the parent-child relationships between specifications on a project. The graphical paradigm can make it very difficult to show how General Specifications and re-used CI’s relate, so must be interpreted with caution.
Spiral Development
A developmental strategy in which each iteration of specification, design and verification will be taken based on the results of the prior step. In effect, a voyage of discovery lived “in the moment”, taking whichever fork in the road makes sense at the time. Contrast with incremental development. In spiral development, knowing where we want... read more
Stable
“Stability” is a condition in which a system’s rates of change with respect to one or more independent variables are bounded. The term is used in many contexts and may seem to have different definitions in each, but they all simplify to something very close to this one.
Standard
A set of processes and practices to accomplish some repeated non-project-specific type of task to some level of quality. Contrast with Specification.
Standup Meeting
If anybody gets tired enough to sit down, you’re doing it wrong.
State
A particular combination of values for a defining set of mutually independent parameters by which some system or circumstance is modeled. The parameters are sometimes referred to as “state variables”. In the sense of how the word “value” is used herein, a state is more accurately defined as some combination of ranges on a set... read more
Statement of Work (SoW)
Make your life simple. Go read MIL-HDBK-245. Unless otherwise specified in the contract, the precedence of a SoW is lower than that of the T&C, but higher than that of a Specification.
States and Modes
The argument over the specifics of this definition is the single biggest time-waster in System Engineering. If only the current specification practices did not require us to define states and modes in the specification… See also state, mode, and busywork.
Stockable Part
A part that is (or can be) be manufactured in advance of need and stored for subsequent sale as being interchangeable with any other of the same part number.
Subcontract
A contract that is contractually and financially subordinate to some other contract (e.g., a Prime Contract) that governs its objectives, practices, and disbursement of funds.
Subject Matter Expert (SME)
Usually, the person who actually understands the technical material of interest. But not always, and that can cause a whole lot of trouble.
Supplier
A source of hardware, software, or services that can generally be exchanged for currency.
Support Equipment
Hardware or software having characteristics not directly needed to comply with requirements that are operationally relevant to the End User, but is necessary (because of the target system’s design features) to deliver, protect, or adapt hardware (or software) during one or more phases of its lifecycle. Support Equipment is often developed in order to adapt... read more
Surrogate
A situation where a technical characterization having direct relevance has been replaced by one having contrived relevance, usually by way of analytical inference. Surrogation is most commonly seen in the context of technical requirements where, in the legacy, they’re sometimes known as “in-lieu-of” requirements. In some cases, the surrogate can be construed as a Similarity Parameter. Contrast with... read more
Synthesis
Synthesis is the process of constituting a thing (which may, or may not, be concrete) from individual parts, imposing relationships between them. Contrast with analysis, design and decomposition.
System
Although many definitions have been proposed by various SE groups, I see little to be gained in comparison to standard dictionary1 definitions: 1) A complex unity formed of many often diverse parts subject to a common plan or serving a common purpose; 2) An aggregation or assemblage of objects joined in regular interaction or interdependence:... read more
System Design Review (SDR)
In the legacy a review held to determine whether “big picture” requirements were individually and collectively feasible to a degree sufficient to warrant expenditure of further government funds. SDR usually corresponded to an A-Spec, and was therefore a government internal event. More recently, it is something else altogether.
System Engineering “V”
A crude depiction of the notion that, as time goes by, System Engineering practices deal with smaller and smaller pieces of the system…but, eventually, they start stitching things back into bigger chunks. I have significant issues with the “V” notion as a primary training tool and process descriptor because I don’t think it describes the... read more
System Engineering (SE)
Historically, we used SE in reference to two distinct concepts1: Systematic Engineering: repeatable processes for which management 2 has a rational expectation that individual skills and expertise do not dominate their ability to audit a project’s technical status3. This notion derives from the reality that Engineering typically doesn’t own the money it spends, and... read more
System Management Plan (SMP)
A subset of the information of a SEMP, excluding the technically relevant aspects of management and, therefore, having less project specificity. That is, it pretty much leaves Engineering out of things.
System Requirements Review (SRR)
In legacy practices, a review held within the government to determine whether A-specs adequately assigned technical requirements to the various government entities that would over-see the contractors of a large project (which may, or may not, be part of a single government program). In modern uses, an excuse to make it look as if we... read more
Systems Engineering Management Plan (SEMP)
A SEMP is a project-specific plan that sequences the important activities of a program, with particular emphasis on provisions for oversight and mid-course correction. In this context, “sequencing” means that the SEMP might lay constraints on certain activities such that they are predicated on successful progress on other activities. Such constraint may be of any... read more