# These slides should give an overview of the sofware architecture, and what its role is. # Why and when is sofware architecture important. # In other words: sofware architecture in a nutshell ! Overview of Sofware Architecture Sofware Architecture VO (706.706) Roman Kern 2020-10-04 Institute for Interactive Systems and Data Science, Graz University of Technology 1 # In English, one refers to “it isn’t rocket science”, as if building rockets is Overview - Motivation the most complex task there is. # Now, let’s look, what could possibly the most complex part here… # Ariane 5 (4th June 1996) crash due to a sofware error: # https://www.youtube.com/watch?v=PK yguLapgA Sofware Development in General Sofware entities are more complex for their size than perhaps any other human construct, because no two parts are alike (at least above the statement level). If they are, we make the two similar parts into one… In this respect sofware systems differ profoundly from computers, buildings, or automobiles, where repeated elements abound. —Brooks, 1986 2 # I.e., the most important word in the context of sofware architecture: Com- Overview - Motivation plexity! # … this also the explanation, why big sofware projects appear to fail ofen. # There it also follows, that building complex systems is an team effort, and the sofware architect plays an vital role here. The big challenge of sofware development and sofware architecture: ⇒ Complexity (in various forms) Hint of a solution The technique of mastering complexity has been known since ancient times: Divide et impera (Divide and Rule). —Dijkstra, 1965 3 # There are also a number of great online resources, please have a look at Resources for Sofware Architecture the course website for links to a few selected ones! Books on sofware architecture • A Sofware Architecture Primer by Reekie and McAdam • Sofware Architecture in Practice by Bass, Kazman and Clemens • The Process of Sofware Architecting by Eeles and Cripps • Big Data: Principles and Best Practices of Scalable Realtime Data Systems by Marz and Warrren 4
# Ofen used analogy w.r.t. to sofware architecture, especially when we Definitions of Sofware Architecture need sofware architecture : # For building a garden shell, one does not need a sophisticated architecture. # … but if one wants to build a skyscraper, this changes (need to take into account, many separate aspects: statics, plumbing, heating, elevators, es- cape paths, …) Definition of sofware architecture • http://www.sei.cmu.edu/architecture/start/glossary/community.cfm • 100+ different definitions 5 — Booch; “Handbook of Sofware Architecture” Definitions of Sofware Architecture Architecture is in Every System Ultimately, every sofware-intensive system has an architecture, be it intentional or accidental . Every such architecture serves to hold back the forces upon that system in a manner that is functional, economical and elegant. – Booch 2009 6 # In real life it is an ongoing effort throughout the project Sofware Architecture Process # Sofware architects work together with other specialists, e.g., business an- alysts are responsible to collect and also to weight requirements . (Over-)Simplified version of the sofware development process 1. Collect requirements • What should the sofware do? 2. System architecture design • What are the system components? • How do they interact? 3. Implement the system • Programming, documentation, testing, … 4. Deliver the system • Deployment Complimentary to this there are additional tasks • Project management & administration • Marketing, etc. 7 # E.g., for the practical part it would be realistic to the change the require- Sofware Architecture Process ment during the course (but will not happen). In practice the sofware development process is more complex • Many sofware development methodologies (e.g. waterfall vs. agile) • Many types of type of sofware types (e.g. projects vs. products) • Sofware architecture takes place during the whole process • But with different emphasis • In practice the requirements change; the setings change; the priorities change • It is a sign of good architecture that it remains relatively stable 8
# Some make a distinction b/w architecture and design. Tasks of the Sofware Architecture Part of sofware architecture • Architecture on a high level • Analyse the context (e.g. requirements, available skills) • Design the structure of the system (e.g. components and their relationship) • Design the behaviour of the system (e.g. sequence of operations) • Define the environment (e.g. select libraries, deployment) NOT part of sofware architecture • Low-level design • Class and variable names • Implementation of algorithms • Selection of data structures 9 # In general there is no common agreement, which language to use, i.e., Sofware Architecture Documentation there is not one single standard for how to formalise the architecture. # In this course a simple language will be presented (more simple than UML). The output of the sofware architecture • Documentation of the architecture • Architecture description language (ADLs) • Document the architecture in a formal way • Typically graphical syntax • Alternatively, existing programming languages have been adapted for architecture specification • Also document the design decisions • Why has a certain decision being made? 10 Stakeholders Definition Stakeholder A stakeholder is an individual, team, or organisation (or classes thereof) with interests in, or concerns relative to a system. – IEEE 1471 2000 11 Stakeholders Influence of stakeholders on the architect and architecture 12
Sofware Architecture Goals Balance out the stakeholders needs • Qality atributes (e.g. usability, security) • System administrators (e.g. ease of administration) • Marketing (e.g. competitive features) • Cost & schedule (e.g. deliver on time to the client) • Developers (e.g. clear requirements) • Project management • Deployment & maintenance ⇒ Functional and non-functional requirements 13 # Coplien et al. Organizational Paterns of Agile Sofware Development. Sofware Architecture Aspects Additional factors that influence the architecture • Teams • Skills • Existing tools and off-the-shelf components • Elegant solution Geographically dispersed teams The architectural partitioning should reflect the geographic partitioning, and vice versa. Architectural responsibilities should be assigned so decisions can be made (geographically) locally. – Coplien, 2005 14 Sofware Architecture What is sofware architecture? • … a science? • Established series of conferences and journals • … an art? • At least it requires a considerable amount of creativity • … an engineering discipline? • What this course is about ⇒ All of the above. 15 # Note: Comparison with film: architect = director, project manager = pro- Sofware Architect ducer. Definition Sofware Architect [An architect is] the person, team, or organisation responsible for systems architecture. – IEEE 1471 2000 ⇒ Sofware architect is a role , i.e. it could be a group of people, or a single person could have additional roles in the project (e.g., project manager) 16
# In fact, many sofware architects have been hardcore hackers. Sofware Architect # Architects sometimes get down to the details (to gain respect from devel- opers). # Many technical people are scared by politics (b/w ambiguities), but e.g., people want to be treated differently. A sofware architect need to • … understand the sofware development process • … understand the business domain • … needs design skills • … needs programming skills • … need to understand (organisational) politics 17 — Kruchten, 1999, The architects: the sofware architecting team. Sofware Architect Sofware architecture skills One does not acquire design prowess overnight; instead, such skill is the result of years of experience . Even expert designers look back on their early work and shudder at how bad it was. As with every other skill, one must practise design in order to obtain proficiency. – Coplien, 2005 Sofware architecture life The life of a sofware architect is a long and rapid succession of suboptimal design decisions taken partially in the dark. – Kruchten, 1999 18 # Now, since complexity is the big challenge for sofware architecture, Sofware Architecture Approaches # … what tactics are there to address these challenges? Need to cut down the complexity • Top down • Start with the high level requirements • Botom up • Start with the existing infrastructure (e.g. existing components, libraries) 19 # Boing 747, 6 million parts, 75k engineering drawings . Sofware Architecture Approaches # Rozanski, Sofware Systems Architecture: Working with stakeholders Us- ing Viewpoints and Perspectives. Need to cut down the complexity • Organise the architecture according to views • Each view has a target audience • Each view might represent a perspective (e.g. security perspective) • Each view has one or more models • Model are typically diagrams • Plus additional documentation Perspective An architectural perspective is a collection of activities, tactics, and guidelines that are used to ensure that a system exhibits a particular set of related quality properties that require considerations across a number of the system’s architectural views. – Rozanski, 2005 20
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