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22 UML design from code. In certain cases, the whole program can be generated from a complete UML description. The UML story illustrates a marked trend in software evolution, from programmers writing procedural code to programmers writing declarative program specifications, which are then 'understood' by a suitable generic processor and turned into procedural code. Topic Declarative bit Processor Non-declarative approach Datahandling using a program The file containing the data The program written to process the data Mapping The map The human brain (able to find a path from A to B, for example) Electronic circuits Spreadsheet A computer-based representation of the circuit (resistor R1 connected to capacitor C3, etc) The spreadsheet itself (i.e. the spreadsheet it is when saved to file: the .xls file). Logic The logic programming 'program' (facts and rules) (see Appendix A2.3) Software tools able to: - simulate the behaviour of the circuit; - prepare a circuit layout for a printed circuit board; - calculate the cost of the circuit; - calculate the heat budget of the circuit. The spreadsheet software, e.g. Microsoft Excel. The logic programming interpreter, e.g. Prolog. Write a program which contains the data in the program itself. Give instructions about how to get from A to B. Write a program for each circuit for each task. E.g. one program would be needed to simulate the behaviour of a specific circuit. Write a program to do the calculations. Difficult to conceive doing using conventional programming.. Advantages of a declarative approach Separate data from program. Therefore same data can be analysed by different programs; same program can be used to analyse different datasets. Map can be used to get from many points to many other points. User constructs a circuit in intuitive terms (resistors, capacitors, etc, and their connections). The one design can be processed by multiple tools. Each tool can be used for all possible circuits, therefore huge savings in effort. Greater ease of use. Support tools (e.g. graphics; immediate update of values). Only feasible way of tackling problems involving logic-based reasoning. Table 5.2 Summary comparison of declarative and procedural software architectures
23 5.5 What are the benefits of greater declarativeness? The declarative approach is generally closer to the way we think about the world. We usually separate knowledge about the world (as facts and rules) from things we can do with that knowledge (reasoning). A declarative approach generally gives more flexibility. A procedural program (recipe) can usually be used for only one purpose. A declarative body of knowledge can be used in many different ways, to answer a wide range of different problems. A declarative body of knowledge generally consists of independent fragments, each of which can be treated separately (e.g. in checking whether it is true or not). A procedural document needs to be treated as a whole, making it more error-prone and difficult to debug. Declarative Use knowledge in multiple ways Low efficiency (though not necessarily true) High modifiability High cognitive adequacy (close to the way we think) Higher level of abstraction Independent collection of facts Easy to validate Transparent Procedural Use knowledge one way High efficiency Low modifiability Low cognitive adequacy (less intuitive way of thinking) Lower level of abstraction A composite whole, difficult to decompose. Hard to debug Black-box Table 5.3 Relative merits of declarative and procedural approaches 5.6 Conclusion In many areas, a declarative approach represents a real and increasingly-used alternative to approaches based on conventional programming. It offers significant benefits, in terms of increased flexibility, transparency and intuitiveness. In the following section, we will begin to explore its relevance to modelling, by comparing the procedural and declarative representation of a simple ecological model. Sources Some points relating to the declarative:procedural divide have been taken from the following sources: http://www.uiowa.edu/~c07p200/handouts/declarative_procedural.html http://computing.unn.ac.uk/staff/cgpb4/prologbook/node11.html http://ai.eecs.umich.edu/cogarch2/prop/declarative-procedural.html http://www.cs.rochester.edu/u/kyros/Courses/CS242/Lectures/Lecture-14/tsld003.htm http://www.cs.cornell.edu/Info/Projects/NuPrl/cs611/fall94notes/cn2/subsection3_1_2.html http://www.psy.vanderbilt.edu/faculty/blake/STIC/memory.html http://www.adass.org/adass/proceedings/adass00/reprints/O6-03.pdf
Page 1 and 2: 1 Position Paper on Declarative Mod
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Page 15 and 16: 15 LAMOS: Landscape Modelling Shell
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Page 25 and 26: 25 6.2 Mathematical description The
Page 27 and 28: 27 6.4 Representation of the model
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Page 43 and 44: 43 and run as a stand-alone model (
Page 45 and 46: 45 Desktop temperature = graph(time
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Page 49 and 50: 49 Example 2: Generating audio desc
Page 51 and 52: 51 8.4 Conclusions The aims of this
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Page 69 and 70: 69 Acknowledgements and declaration
Page 71 and 72: 71 Forrester, J.W. (1971) World Dyn
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73 URLs: (Web links) ACSL Advanced
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75 Glossary See "URLs: Web links" a
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77 Appendix 1. The Modelica, MODCOM
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79 Appendix 2. A brief introduction
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81 bank vole Clethrionomys glareol
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