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Mary Shaw And David Garlan Software Architecture Pdf

mary shaw and david garlan software architecture pdf

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The Software Architecture

Software architecture refers to the fundamental structures of a software system and the discipline of creating such structures and systems. Each structure comprises software elements, relations among them, and properties of both elements and relations. Software architecture is about making fundamental structural choices that are costly to change once implemented.

Software architecture choices include specific structural options from possibilities in the design of the software. For example, the systems that controlled the Space Shuttle launch vehicle had the requirement of being very fast and very reliable.

Therefore, an appropriate real-time computing language would need to be chosen. Additionally, to satisfy the need for reliability the choice could be made to have multiple redundant and independently produced copies of the program, and to run these copies on independent hardware while cross-checking results. Documenting software architecture facilitates communication between stakeholders , captures early decisions about the high-level design, and allows reuse of design components between projects.

Opinions vary as to the scope of software architectures: [5]. There is no sharp distinction between software architecture versus design and requirements engineering see Related fields below. They are all part of a "chain of intentionality" from high-level intentions to low-level details. Multitude of stakeholders: software systems have to cater to a variety of stakeholders such as business managers, owners, users, and operators.

These stakeholders all have their own concerns with respect to the system. Balancing these concerns and demonstrating that they are addressed is part of designing the system. Separation of concerns : the established way for architects to reduce complexity is to separate the concerns that drive the design. Architecture documentation shows that all stakeholder concerns are addressed by modeling and describing the architecture from separate points of view associated with the various stakeholder concerns.

Quality-driven: classic software design approaches e. Jackson Structured Programming were driven by required functionality and the flow of data through the system, but the current insight [4] : 26—28 is that the architecture of a software system is more closely related to its quality attributes such as fault-tolerance , backward compatibility , extensibility , reliability , maintainability , availability , security, usability, and other such — ilities.

Stakeholder concerns often translate into requirements on these quality attributes, which are variously called non-functional requirements , extra-functional requirements, behavioral requirements, or quality attribute requirements. Recurring styles: like building architecture, the software architecture discipline has developed standard ways to address recurring concerns. These "standard ways" are called by various names at various levels of abstraction. Common terms for recurring solutions are architectural style, [11] : — tactic, [4] : 70—72 reference architecture [13] [14] and architectural pattern.

Conceptual integrity: a term introduced by Fred Brooks in The Mythical Man-Month to denote the idea that the architecture of a software system represents an overall vision of what it should do and how it should do it. This vision should be separated from its implementation.

The architect assumes the role of "keeper of the vision", making sure that additions to the system are in line with the architecture, hence preserving conceptual integrity. Cognitive constraints: an observation first made in a paper by computer programmer Melvin Conway that organizations which design systems are constrained to produce designs which are copies of the communication structures of these organizations. As with conceptual integrity, it was Fred Brooks who introduced it to a wider audience when he cited the paper and the idea in his elegant classic The Mythical Man-Month , calling it "Conway's Law.

Software architecture is an "intellectually graspable" abstraction of a complex system. The comparison between software design and civil architecture was first drawn in the late s, [18] but the term "software architecture" did not see widespread usage until the s. Although the term "software architecture" is relatively new to the industry, the fundamental principles of the field have been applied sporadically by software engineering pioneers since the mids.

Early attempts to capture and explain software architecture of a system were imprecise and disorganized, often characterized by a set of box-and-line diagrams. Software architecture as a concept has its origins in the research of Edsger Dijkstra in and David Parnas in the early s. These scientists emphasized that the structure of a software system matters and getting the structure right is critical. During the s there was a concerted effort to define and codify fundamental aspects of the discipline, with research work concentrating on architectural styles patterns , architecture description languages , architecture documentation , and formal methods.

Research institutions have played a prominent role in furthering software architecture as a discipline. Mary Shaw and David Garlan of Carnegie Mellon wrote a book titled Software Architecture: Perspectives on an Emerging Discipline in , which promoted software architecture concepts such as components , connectors, and styles.

The University of California, Irvine 's Institute for Software Research's efforts in software architecture research is directed primarily in architectural styles, architecture description languages, and dynamic architectures. This reflects the relationship between software architecture, enterprise architecture and solution architecture. There are many activities that a software architect performs. A software architect typically works with project managers, discusses architecturally significant requirements with stakeholders, designs a software architecture, evaluates a design, communicates with designers and stakeholders, documents the architectural design and more.

Architectural analysis is the process of understanding the environment in which a proposed system will operate and determining the requirements for the system. The input or requirements to the analysis activity can come from any number of stakeholders and include items such as:.

The outputs of the analysis activity are those requirements that have a measurable impact on a software system's architecture, called architecturally significant requirements.

Architectural synthesis or design is the process of creating an architecture. Given the architecturally significant requirements determined by the analysis, the current state of the design and the results of any evaluation activities, the design is created and improved. Architecture evaluation is the process of determining how well the current design or a portion of it satisfies the requirements derived during analysis.

An evaluation can occur whenever an architect is considering a design decision, it can occur after some portion of the design has been completed, it can occur after the final design has been completed or it can occur after the system has been constructed. Architecture evolution is the process of maintaining and adapting an existing software architecture to meet changes in requirements and environment.

As software architecture provides a fundamental structure of a software system, its evolution and maintenance would necessarily impact its fundamental structure. As such, architecture evolution is concerned with adding new functionality as well as maintaining existing functionality and system behavior.

Architecture requires critical supporting activities. These supporting activities take place throughout the core software architecture process. They include knowledge management and communication, design reasoning and decision making, and documentation. Software architecture supporting activities are carried out during core software architecture activities. These supporting activities assist a software architect to carry out analysis, synthesis, evaluation, and evolution.

For instance, an architect has to gather knowledge, make decisions and document during the analysis phase. Software architecture description involves the principles and practices of modeling and representing architectures, using mechanisms such as architecture description languages, architecture viewpoints, and architecture frameworks.

Software architecture descriptions are commonly organized into views , which are analogous to the different types of blueprints made in building architecture. The viewpoint specifies not only the concerns framed i. A framework is usually implemented in terms of one or more viewpoints or ADLs.

An architectural pattern is a general, reusable solution to a commonly occurring problem in software architecture within a given context. Architectural patterns are often documented as software design patterns. Following traditional building architecture, a 'software architectural style' is a specific method of construction, characterized by the features that make it notable" architectural style.

An architectural style defines: a family of systems in terms of a pattern of structural organization; a vocabulary of components and connectors, with constraints on how they can be combined. Architectural styles are reusable 'packages' of design decisions and constraints that are applied to an architecture to induce chosen desirable qualities.

Some treat architectural patterns and architectural styles as the same, [35] some treat styles as specializations of patterns. What they have in common is both patterns and styles are idioms for architects to use, they "provide a common language" [35] or "vocabulary" [33] with which to describe classes of systems.

There are also concerns that software architecture leads to too much Big Design Up Front , especially among proponents of agile software development. A number of methods have been developed to balance the trade-offs of up-front design and agility, [36] including the agile method DSDM which mandates a "Foundations" phase during which "just enough" architectural foundations are laid.

IEEE Software devoted a special issue to the interaction between agility and architecture. Software architecture erosion or "decay" refers to the gap observed between the planned and actual architecture of a software system as realized in its implementation. As an example, consider a strictly layered system, where each layer can only use services provided by the layer immediately below it.

Any source code component that does not observe this constraint represents an architecture violation. If not corrected, such violations can transform the architecture into a monolithic block, with adverse effects on understandability, maintainability, and evolvability.

Various approaches have been proposed to address erosion. Within these broad categories, each approach is further broken down reflecting the high-level strategies adopted to tackle erosion. These are process-oriented architecture conformance, architecture evolution management, architecture design enforcement, architecture to implementation linkage, self-adaptation and architecture restoration techniques consisting of recovery, discovery, and reconciliation.

There are two major techniques to detect architectural violations: reflexion models and domain-specific languages. Reflexion model RM techniques compare a high-level model provided by the system's architects with the source code implementation.

There are also domain-specific languages with a focus on specifying and checking architectural constraints. Software architecture recovery or reconstruction, or reverse engineering includes the methods, techniques, and processes to uncover a software system's architecture from available information, including its implementation and documentation.

Architecture recovery is often necessary to make informed decisions in the face of obsolete or out-of-date documentation and architecture erosion : implementation and maintenance decisions diverging from the envisioned architecture.

This is a part of subjects covered by the software intelligence practice. Architecture is design but not all design is architectural. There are no rules or guidelines that fit all cases, although there have been attempts to formalize the distinction. For example, the client—server style is architectural strategic because a program that is built on this principle can be expanded into a program that is not client—server—for example, by adding peer-to-peer nodes. Requirements engineering and software architecture can be seen as complementary approaches: while software architecture targets the ' solution space ' or the 'how', requirements engineering addresses the ' problem space ' or the 'what'.

Both requirements engineering and software architecture revolve around stakeholder concerns, needs and wishes. There is considerable overlap between requirements engineering and software architecture, as evidenced for example by a study into five industrial software architecture methods that concludes that "the inputs goals, constraints, etc.

From Wikipedia, the free encyclopedia. High level structures of a software system. Main article: Software architecture description. Main article: Architecture description language. Main article: View model. Main article: Architecture framework. Main article: Architectural pattern. Main article: Agile development. Main article: Software architecture recovery. Main article: Software design.

Software Engineering Reading List

References :. Software Architecture in Practice , L. Bass, P. Kazman, Addison Wesley. Non-Functional Requirements in Software Engineering ,. Common software architectural styles, elements and connectors. Decomposition and composition of software functionality.

Software Architecture: Perspectives on an Emerging Discipline

Software Architecture: Perspectives on an Emerging Discipline

Alternative formats. Appropriate for special topic courses on Software Architecture or as an inexpensive supplement to software engineering courses.


Explore more content. An Introduction to Software Architecture. Cite Download As the size of software systems increases, the algorithms and data structures of the computation no longer constitute the major design problems. When systems are constructed from many components, the organization of the overall system—the software architecture—presents a new set of design problems. This level of design has been addressed in a number of ways including informal diagrams and descriptive terms, module interconnection languages, templates and frameworks for systems that serve the needs of specific domains, and formal models of component integration mechanisms. In this paper we provide an introduction to the emerging field of software architecture.

More advice here: Ambler, S. In software-intensive systems, technical debt consists of design or implementation constructs that are expedient in the short term, but set up a technical context that can make a future change more costly or impossible. Technical debt is a contingent liability whose impact is limited to internal system qualities, primarily maintainability and evolvability. At a recent workshop, at XP , we looked into practices that support scaling up agile, and in particular the role of architecture. These three structures must be kept aligned over time, especially to support an agile development style. We can examine the alignment of these structures from the perspective of A and the role of the architect in an agile software-development organization. The relationship of A to S is also known as socio-technical congruence and has been extensively studied, especially in the context of global, distributed software development.

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