Legacy software systems are typically complex, geriatric, and difficult to change, having evolved over decades and having passed through many developers. Nevertheless, these systems are mature, heavily used, and constitute massive corporate assets. Migrating such systems to modern platforms is a significant challenge due to the loss of information over time. As a result, we embarked on a research project to design and implement an environment to support software migration. In particular, we focused on migrating legacy PL/I source code to C++, with an initial phase of looking at redocumentation strategies. Recent technologies such as reverse engineering tools and World Wide Web standards now make it possible to build tools that greatly simplify the process of redocumenting a legacy software system. In this paper we introduce the concept of a software bookshelf as a means to capture, organize, and manage information about a legacy software system. We distinguish three roles directly involved in the construction, population, and use of such a bookshelf: the builder, the librarian, and the patron. From these perspectives, we describe requirements for the bookshelf, as well as a generic architecture and a prototype implementation. We also discuss various parsing and analysis tools that were developed and integrated to assist in the recovery of useful information about a legacy system. In addition, we illustrate how a software bookshelf is populated with the information of a given software project and how the bookshelf can be used in a program-understanding scenario. Reported results are based on a pilot project that developed a prototype bookshelf for a software system consisting of approximately 300K lines of code written in a PL/I dialect.

The software bookshelf

The EU and European governments have been funding product family development projects for years. This article overviews the different projects, the topics each has addressed, and the main results obtained thus far.

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Software product families in Europe: the Esaps & Cafe projects

Statics Introduction, R. Hibbeler Force Systems Resultants and Equilibrium, R. Hibbeler Centroids and Distributed Loads, W.D. Pilkey and L. Kitis Moments of Inertia, J.L. Meriam Mechanics of Materials Introduction, T. Anderson Reactions, T. Anagnos Bending Stresses in Beams, J. Gere Shear Stresses in Beams, J. Gere Shear and Moment Diagrams, G. Buchanan Columns, L. Zachary and J. Ligon Pressure Vessels, E. Livingston and R.J. Scavuzzo Axial Loads and Torsion, N.R. Bauld, Jr. Fracture Mechanics, T. Anderson Dynamics and Vibration Introduction, B. Karnopp Dynamics of Particles: Kinematics and Kinetics, B. Karnopp Dynamics of Rigid Bodies: Kinematics and Kinetics, A. Zeid and R. Beck Free Vibration, Natural Frequencies, and Mode Shapes, D. Mendelsohn Forced Vibrations, A. Leissa Lumped versus Distributed Parameter Systems, B. Ovunc Applications of Structural and Dynamic Principles, A. Kalinowski Computer Simulation and Nomographs, D. Inman Test Equipment and Measuring Instruments, T. Baird Kinematics and Mechanisms Introduction, B. Ravani Linkages and Cams, J.M. McCarthy and G.L. Long Tribology: Friction, Wear, and Lubrication, B. Bhushan Machine Elements, G. Pennock Crankshaft Journal Bearings, P.K. Subramanyan Fluid Sealing in Machines, Mechanical Devices, and Apparatus, A. Lebeck Structures Introduction, J. McCormac Loads, P. Gergely Wind Effects, T. Reinhold and B. Sill Earthquake Effects, M. Ravindra and J. Shipp Structural Analysis, R. Sexsmith and T. Cigic Structural Steel, W. Segui Concrete, E. Nawy Timber, D. Breyer Masonry Design, J. Amrhein Fluid Mechanics Introduction, F. Kreith Incompressible Fluids, A. McDonald Compressible Fluids, J. Hoffman Rheology of Non-Newtonian Fluids, D. Doraiswamy Airfoils/Wings, B. Munson and D. Cronin Boundary Layers, E. Braun and P.-L. Wang Valves, J.P. Tullis Pumps and Fans, R. Boehm Two-Phase Flow, R. Lahey Basic Mixing Principles for Various Types of Fluid Mixing Applications, J. Oldshue Fluid Measurements, S.A. Sherif Thermodynamics and Heat Transfer Introduction, F. Kreith The First Law of Thermodynamics, R. Sonntag Second Law of Thermodynamics and Entropy, N. Lior Thermodynamics of Solutions, S. Sandler and H. Orbey Thermodynamics of Surfaces, W. Krantz Phase Equilibrium, B. Kyle Thermodynamic Cycles, W.J. Cook Heat Transfer, Y. Bayazitoglu and U. Sathuvalli Heat Exchangers, M. Ohadi Combustion, R. Hecklinger Air Conditioning, V. Goldschmidt Refrigeration and Cryogenics, R. Barron Heat Transfer to Non-Newtonian Fluids, E.F. Matthys Heat Pipes, L. Swanson Separation Processes Introduction, K. Timmerhaus Distillation, J.R. Fair Absorption and Stripping, W.M. Edwards and J.R. Fair Extraction, V. Van Brunt Adsorption, S. Sircar Crystallization and Evaporation, R. Bennett Membrane Separations, D. Woods, D. Walker, and W. Koros Fluid Particle Separation, S. Chaing and D. He Other Separation Processes, W. Corder and S. Hanson Fuels and Energy Conversion Introduction, F. Kreith Fuels, S. Moustafa Solar Systems, J.M. Chavez, E.M. Richards, and A. Van Arsdal Internal Combustion Engines, A. Kornhauser Gas Turbines, L.S. Langston and G. Opdyke, Jr. Nuclear Power Systems, D.M. Woodall Power Plants, M. El-Wakil Wind Turbines, A. Swift and E. Moroz Hydraulic Turbines, R. Arndt Steam Turbines, G. Shibayama and R. Franceschinis Cogeneration, D. Cooke Electric Machines, E.K. Stanek Kinetics and Reaction Engineering Introduction, J. Falconer Reaction Kinetics, K.H. Lin Chemical Reaction Engineering, H.S. Fogler Scale-Up of Chemical Reaction Systems from Laboratory to Plant, J.B. Cropley Geotechnical Introduction, M. Harr Soil Mechanics, B. Das Transportation Introduction, K. Sinha Transportation Planning, M. Meyer Design of Transportation Facilities, M. Meyer Operations and Environmental Impacts, P.W. Shuldiner and K.B. Black Transportation Systems, P. Schonfeld Transportation Safety Analysis, T. Khalil Coastal and Ocean Engineering Introduction, W. Wood Shallow Water and Deep Water Engineering, J. Herbich Environmental Systems and Management Introduction, R. Jacko Drinking Water Treatment, A. Amirtharajah and S.C. Jones Air Pollution, F.C. Alley and C.O. Cooper Wastewater Treatment and Disposal, H. Peavy Solid Wastes, R. McKinney Hazardous Waste Management, H.M. Cota and D. Wallenstein Soil Remediation, B.M. Kim and A. Shapiro Water Resources Engineering Introduction, J. Delleur Hydraulics, B. Hauser Hydrology, V. Singh Sedimentation, E.V. Richardson Linear Systems and Models Introduction, R. Ziemer Transfer Functions and Laplace Transforms, C.N. Dorny Block Diagrams, A. Sage Signal Flow Graphics, A. Kraus Linear State-Space Models, B. Schimel and W. Grantham Frequency Response, P. Neudorfer and P. Gehlen Convolution Integral, R. Ziemer Stability Analysis, R. Stefani Z-Transforms and Digital Systems, R. Johansson Circuits Introduction, W.-K. Chen Passive Components, H. Domingos RL, RC, and RLC Circuits, M. Ciletti Node Equations and Mesh Equations, J. Svoboda Sinusoidal Excitation and Phasors, M. Rashid Three-Phase Circuits, N. Balabanian Filters, Passive, A. Rosa Power Distribution, R. Broadwater, A. Sargent, and R. Lee Grounding and Shielding, W. Duff Electronics Introduction, T. Jackson Operational Amplifiers, P. Hurst Active RC Filters, M. Soderstrand Diodes and Transistors, S. Soclof Analog Integrated Circuits, S. Soclof Optoelectronic Devices, P. Bhattacharya Power Electronics, K. Rajashekara A/D and D/A Converters, J. Hamann Superconductivity, K. Delin and T. Orlando Digital Systems Introduction, V. Oklobdzija Logic Devices, R. Sandige Counters and State Machines (Sequencers), B. Wilkinson Microprocessors and Microcontrollers, F. Hill Memory Systems, R. Sandige Computer-Aided Design and Simulation, M. Ciletti Logic Analyzers, S. Mourad and M.S. Haydt Communications and Signal Processing Introduction, H.V. Poor Transforms and Fast Algorithms, A. Poularikas Digital Filters, B. Bomar and L.M. Smith Modulation and Detection, H.V. Poor Coding, S. Miller and L. Couch II Computer Communication Networks, J. Daigle Satellites and Aerospace, S.W. Fordyce and W.W. Wu Mobile and Cellular Radio Communications, T. Rappoport, R. Muhamed, M. Buehrer, and A. Doradla Optical Communications, J. Palais Computers Introduction, V. Oklobdzija Computer Organization: Architecture, V. Oklobdzija Operating Systems, L.-F. Cabrera Programming Languages, D. Volpano Input/Output Devices, R. Freitas Memory and Mass Storage Systems, P. Chen Measurement and Instrumentation Introduction, W. von Maltzahn Sensors and Transducers, R. Smith Measurements and Accuracy, S. Harrison Signal Conditioning, S. Dyer Telemetry, S. Horan Recording Instruments, W. Owens Bioinstrumentation, W. von Maltzahn and K. Meyer-Waarden Surveying Introduction, J. McCormac Quality Control, B. van Gelder Elevation, S. Johnson Distance Measurements, R.B. Buckner Directions, B. Dewitt Photogrammetry and Topographic Mapping, J. Bethel Surveying Computations, B. van Gelder Satellite Surveying, B. van Gelder Surveying Applications for Geographic Information Systems, J. Thompson Remote Sensing, R. Kiefer and T. Lillesand Control Systems Introduction, F. Raven Feedback, W. Brogan Root Locus, W. Brogan Nyquist Criterion and Stability, N. Nise System Compensation, F. Raven Process Control, T. Marlin Digital Control, R. Jacquot Robots and Control, R. Bonitz and T.C. Hsia State Variable Feedback, T. Vincent Manufacturing Introduction, F. Kreith Types of Manufacturing, R. Schonberger Quality, M. Stephens and J. Kmec Flexible Manufacturing, A. Kusiak and C.-X. Feng Management and Scheduling, E. Knod, Jr. Design, Modeling, and Prototyping, W. Chapman and A.T. Bahill Materials Processing and Manufacturing Methods, S. Risbud Machine Tools and Processes, Y. Shin Human Factors and Ergonomics, W. Karwowski and B. Jamaldin Pressure and Vacuum, P. Biltoft, C. Borzileri, D. Holten, and M. Traini Food Engineering, R.P. Singh Agricultural Engineering, D. Hills System Reliability, R. Ramakumar Aeronautics and Aerospace Introduction, C. Spitzer Aerodynamics, J. Donovan Stability and Turbulence, R. Hess Computational Fluid Dynamics, R. Agarwal Aerospace Materials, R. June Propulsion Systems, J. Monk Aircraft Performance and Design, F. Hale Spacecraft and Mission Design, W. Fowler Safety Introduction, A.K. Furr Hazard Identification and Control, M. Rahimi Regulations and Standards, A.K. Furr Engineering Economics and Management Introduction, T. Au Present Worth Analysis, W. Short Project Analysis Using Rate-of-Return Criteria, R. Beaves Project Selection from Alternatives, C. Hendrickson and S. McNeil Depreciation and Corporate Taxes, T. Au Financing and Leasing, C. Fazzi Risk Assessment, R. Ruegg Sensitivity Analysis, H. Marshall Life-Cycle Costing, W. Fabrycky and B. Blanchard Project Evaluation and Selection, H. Thamhain Critical Path Method, J. Richards Patents, Copyrights, Trademarks, and Licenses, P. Beck and C. Bordas Materials Engineering Introduction, J. Shackelford Properties of Solids, J. Shackelford Failure Analysis, J. Shackelford Liquids and Gases, B. Poling Biomaterials, R.B. Martin Mathematics Introduction, W.F. Ames General Mathematics Linear Algebra Matrices, G. Cain Vector Algebra and Calculus, G. Cain Complex Variables, G. Cain Difference Equations, W.F. Ames Differential Equations, W.F. Ames Integral Equations, W.F. Ames Approximation Methods, W.F. Ames Integral Transforms, W.F. Ames Chaos, Fractals, and Julian Sets, A. Deliu Calculus of Variations, W.F. Ames Probability and Statistics, Y.L. Tong Optimization, G. Cain Numerical Methods, W.F. Ames Dimensional Analysis, W.F. Ames Computer Graphics Visualization, R. Gallagher Appendix: Mathematical Tables and Formulae Associations and Societies

The Engineering Handbook

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Software product lines in action

The data regarding the components of a software system consists of a large amount of information such as version history, number of lines, defect density, and complexity measures. The ability to quickly grasp a comprehensive view of the evolution and dependencies of such information is the key to making informed decisions about future developments of the system. Managers usually make such decision based only on expert judgement. For help in making such decisions, we can turn to the evolution history of large software systems, which contain a wealth of hidden information. Traditionally, this information is passed on through anecdotes without any supporting analytical data. This paper reports on our attempts to make such information more concrete through information visualization techniques. We present a three-dimensional visual representation for examining a system's software release history. The structure of the system is displayed by 2D or 3D graphs. The historical information is displayed by using time as the third dimension. Colors are used for displaying module properties and their historical changes in the system. A supporting software tool enables not only visualization but also navigation in the 3D space to change the viewpoint, to browse system information, to find interesting patterns and to discover previously unknown relationships among system components.

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Visualizing software release histories: the use of color and third dimension

Large systems need a sound architecture. In our method, we decompose the system into building blocks to make it "future-proof," accommodate functional needs, and minimize system complexity. We organize the system construction along three design dimensions covered by the system architecture: structure, aspects, and behavior. The structure determines the system's decomposition into parts and the relationships between the parts. Aspects model the functional decomposition of the system. Behavior deals with processing that takes place within the system. Of the three dimensions, we consider structure to be the most important. In this dimension, reducing complexity is our main concern. We organize system functionality into four layers, or subsystems. These subsystems are composed of software modules-building blocks-which are the basic software entities in the system architecture. >

Creating architectures with building blocks

At Philips Kommunikations Industrie, a building block development method is used in the construction of telecommunication infrastructure systems. This architectural method has been optimised for the construction of product families. Building blocks are the components of which the software is build. They resemble hardware components by being pre-manufactured components. The building blocks reside in a 'construction set'. The family architecture is based upon a skeleton of generic building blocks. These building blocks are present in (almost) all systems in the family. Different configurations can be obtained by selecting the appropriated application building blocks from the construction set. This paper describes the notions of generic and application building blocks and their use for product families.

J.K. Muller

Papers

Creating architectures with building blocks

Composing product families from reusable components