Quote: successful, large systems tend to be organized in layers or levels of abstraction

Quote: a good design models some aspect of reality. Concepts are classes with inheritance to show relationships. Multiple levels of abstraction [»stroB_1991]

Quote: resource allocation should be organized in levels of abstraction with minimal dependencies between levels

Quote: lowest robot level avoids objects, next layer makes robot wander about, third level encourages exploration [»brooRA1_1991]

Quote: with a structured flow chart can fold the paper to show an abstraction level

Quote: structure an operating system as layers of insensitive, abstract machines

Quote: each operating system level manages a particular type of abstract object [»robiL9_1975]

Quote: CADES design is a series of levels; each level an abstract machine [»pearDJ7_1973]

Quote: a design level tells what must be done by the lower level and how to implement the higher level [»neugW_1982]

Quote: every specification is an implementation of a higher level specification

Quote: good interfaces allow low-level details to change without effecting the higher levels [»rossDT_1970]

Quote: digital computers allow many representational layers; a variable may represent a satellite and in turn be represented by a voltage [»winoT_1986]

Quote: 2-level van Wijngaarden grammars define meta rules that generate BNF rules [»kostCH_1974a, OK]

Quote: level principle--active entities at one level are data structures at a lower level; e.g., process vs. context block [»finkRA_1986]

Quote: Cedar uses system layering to reduce compilation dependencies and increase use of system components [»swinDC7_1985]

Quote: separate the presentation code from domain code; the UI should only display information [»fowlM3_2001]

Quote: stage three of CADES structural modeling is defining the system's levels and functions [»pearDJ7_1973]

Quote: the 'context' layer in Conniver's database shows differences from previous layers [»mcdeDV9_1975]

Quote: an electronic test system may have many levels of specification, e.g., run smoothly, rpms, voltage [»cheaTE_1976]

Quote: the top-down designer creates tree structures; at a level with no shared components [»jackMA_1975]

Quote: portability may measure the representation level of a program; e.g., octal code is not portable [»cbb_1973, OK]

Quote: using MacApp for Intermedia, guarantees common functionality

Quote: one programs for a virtual machine defined by hardware and other software [»parnDL8_1971]

Quote: have ten orders of magnitude between program execution in hours and instruction execution in a microsecond; must have intermediate levels [»dijkEW10_1972]

Quote: hierarchy allows large and complex programs out of simple components; complexity only through number of components and levels [»jackMA_1975]

Quote: need intermediate levels between a program's execution and an instruction's execution; about a 10^10 ratio; bricks to walls is maybe 10^3

Quote: a programmer must bridge a 10^9 ratio in time and space with a single technology; much deeper conceptual hierarchy than ever before [»dijkEW12_1989]

Quote: each level of a hierarchy represents a doubling or more in size; small and medium systems have few levels [»dijkEW10_1972]

Quote: the minimum number of layers in a system is a high-level programming language and hardware; the operating system can be eliminated [»ingaDH9_1982]

Quote: a vast amount of code is required to realize a programmer's intent, often concisely stated [»laruJR5_2004]

Quote: use correctness tools to close the immense gap between code and intent

Quote: end-to-end argument--implement functions at the endpoints of a communication system; do not implement within the communication system unless needed for efficiency [»saltJH11_1984]

Quote: be careful of functions in low-level subsystems; every application will pay for it; limited information to do job efficiently [»saltJH11_1984]

Quote: assign user programs to reserved processes; do not charge time spent in critical sections [»dijkEW2_1971]

Quote: organize a layer as tasks made of subroutines; all interfaces are subroutine calls instead of intertask communication [»clarDD12_1995]

Quote: subsumption architecture for intelligent robots: fixed-topology layers of finite state machines; higher layers can replace or inhibit messages of lower layers [»brooRA1_1991]

Quote: collision control where higher levels restrict free parameters of lower levels [»freuE_1984]

QuoteRef: robiL9_1975 ;;2 levels of abstract machines which only access one level away. Level either transparent to feature or hides feature

Quote: lower levels can't use knowledge about higher levels; but undesired events need higher level information to determine the appropriate action [»parnDL10_1976b]

Quote: a reported undesired event indicates a failure of the previous level's abstract machine

Quote: an undesired event may be propagating downward (i.e., violating virtual machine restrictions) or upward (i.e., reported by lower level) [»parnDL10_1976b]

Quote: use up-calls to transfer incoming network data, user input, or status changes to higher level processes; avoids context switches; used for high-performance networks [»birrAD_1991]

Quote: an upcall calls a higher level function across protection boundaries; an alternative to asynchronous signals [»clarDD12_1995]

Quote: upcalls usually call a higher level function through a procedure variable

Quote: rewriting a downcall protocol as upcalls improved performance and code size by 5-10x [»clarDD12_1995]

Quote: an upcall may asks questions about its service; e.g., ask for further data to append to an outgoing packet [»clarDD12_1995]

Quote: with upcalls, need to separate client data from the level's data; the later must be consistent and unlocked before an upcall occurs [»clarDD12_1995]

Quote: with upcalls, need to either disallow recursive downcalls, restrict downcalls to simple actions/queuing, or restrict downcalls to setting flags [»clarDD12_1995]

Quote: layered abstractions increase the stack data cache footprint, TLB misses, and function call overhead; too many arguments; spectacularly deep call stacks [»smaaB2_2006]