Software Engineering 3156AdministriviaA Bit on Chapter 9MetricsOther MetricsActual EstimationSpecification documentInformal specificationsStructured systems analysisDFDRemaining structured systems analysis stepsOther semiformal techniquesEntity-relationship modeling (ERM)Finite state machinesPetri netsZOther formal techniquesMiscellanyService DiscoveryDNS: Domain Name ServiceDNS (II)Others (I)Others (II)Challenges for service discoveryLDAP: Lightweight Directory Access ProtocolLDAP (II)LDAP 4 UServicesActorsActor states per worldWhat does this mean for you?Software Engineering 31568-Oct-01#10: Classical Specs & Service DiscoveryPhil Gross2AdministriviaVersion 1.0 upKeep the webboard stuff goingTAs3A Bit on Chapter 9Size/cost estimation is painfulObviously necessary in the real worldWe’re puntingTake 4156 to learn details4MetricsLOC–Programming language dependent–Comments?–Tools/throwaway?–Generated code?–How do you estimate LOC?5Other MetricsFunctions points–Data processing oriented–Input, output, and master files–Degrees of influence, Technical Complexity Factors…6Actual EstimationCOCOMO and COCOMO IIBased on statistics gathered from real projectsAwful, but the best we’ve gotAimed at huge software projects7Specification documentContract between client and developerAcceptance criteria–Solution strategy–Keep track of which solutions are kept and those discarded for later justificationCost-benefit analysis8Informal specificationsXhosa!?Mostly proseEasy to screw up and make ambiguous: English sucksMy MTA example from second class9Structured systems analysisStart with Data Flow Diagrams (DFD’s)Show what happens, not howUse stepwise refinement: start with high-level DFD and work down from thereUML state diagram generalization of this10DFDAfter several iterations, quite detailed, but customer can still understandLess data-hiding than object-oriented mechanismsStill useful for formalized contracts11Remaining structured systems analysis stepsDecide, from DFD, what to computerizeDetermine details of data flowsDefine process logicDefine data storesDefine physical resources (files, organization, storage medium, etc.)Determine I/O specsDetermine sizing (CPU, size)Determine hardware requirements12Other semiformal techniquesPSL (problem statement language) and PSA (problem statement analyzer) – computer-aidedSADT (box-and-arrow-based structural analysis and design technique): more refinement than DFDSREM (Software Requirements Engineering Method, pronounced “shrem”): specify conditions for actions to occur; based on finite state machines; has been used for C3I applications by the air force13Entity-relationship modeling (ERM)Looks like a class diagram, no?Predecessor, in a sense14Finite state machinesPrecursor of UML state diagramsStill used in many low-level specification areasNotion of states and transitions formally specifiedUseful in menu-driven UI’s, system designAbove refers to 3-position combo lockHuge example in Schach for elevatorsComp Org…15Petri netsProblem: state machines are weak at handling timing issuesCan use state charts (or state diagrams)Petri nets are state-based, but have tokens in states to allow multiple transitions to happen at the same time (concurrency modeling)16ZZed, not zee!Rather formalized specification languageDifficulty outside the scope of this class–Utilizes set theory, functions, and first-order logicWe’re not covering this, but take a peek in the book17Other formal techniquesEvent-based specification: Communicating Sequential Processes [Hoare, 1985]–A little too complex for us–Nevertheless, we want to consider event models; they’ve become very commonMany others (Anna, Gist, VDM)Active theoretical research (woohoo!)18MiscellanyTesting–Walkthroughs–Inspection against checklist–Correctness-proving for formal specificationsMetrics–Size of DFD, data dictionary, etc.Challenge–Find something that the customer understands yet is good enough for a contract–Sometimes this is impossible: need technical people at customer19Service DiscoveryIt’s no longer just the web anymoreAbstraction of service from network node (or computer)Goal: find a service without hardcoding where it isUse DNS, LDAP, others20DNS: Domain Name ServicePrimary purpose: “discover” machines–“Address record”: for example, www.cs.columbia.edu = 128.59.16.149–Equivalent to an address bookSecondary purpose: advertise mail servers–“Mail server”, or MX record: cs.columbia.edu’s mail is primarily handled by ober.cs.columbia.edu21DNS (II)More recent: user-definable services, using SRV records–Domain controllers–Telephony servers–Generally done on a domain basis: “here’s the service provider for domain X”Tools for DNS–nslookup–host–numerous API’s (resolve r built into sockets)22Others (I)SIP: Session Initiation Protocol: Invented Here!*–http://www.cs.columbia.edu/~hgs/sip–Basic idea: how to find someone to communicate with–Primarily for telephony applications (Caller-ID, Call-Forwarding, etc.)Jini: distributed object-level service discovery–Appliance-aware services: embedded Java23Others (II)SLP (Service Location Protocol)–IETF attempt, generalized SIP–Less successful so far: maybe IPv6?NIS (Network Information Service)–Primarily user authentication, but can generalize–“Mirror” /etc files24Challenges for service discoveryRunning out of IP addresses to host these services on–IPv6Lack of a standardized mechanism–Each service discovery mechanism has its own target applicationsMobile services–Wireless technology: “find” the service physically25LDAP: Lightweight Directory Access ProtocolOne popular solution to general discovery requirementsVery generalized white-pages mechanism–User-definable “schemas”–Common applications are network nodes and usersBased on DAP, X.500Extremely popular–ldap.columbia.edu: try it out…–Lookups are very fast26LDAP (II)We will be using LDAP for several purposes–Discovering server and AI programs on the network–Keeping track of basic user authentication and informationLDAP server already set up on softe.cs.columbia.edu–Code examples will be covered in next week’s recitation–Don’t need the code