5 Part 5: V-Modell Reference Work Products

5.3 Products

5.3.7 Requirements and Analyses

5.3.7.11 Legacy System Analysis

Process module: Enhancement and Migration of Legacy Systems

Responsible: System Architect (when using process module Enhancement and Migration of Legacy Systems)

Purpose

The »Legacy System Analysis is intended to describe the actual state of a system, to provide an understanding for the legacy system and to lay the basis for the further development or migration of system components. The analysis describes functionality, objectives and rough architecture of the legacy system and identifies interactions between the system and its environment. The current »Data Model of the legacy system shall be determined and the data quality shall be assessed in order to provide a basis for the migration.

The »System Architect is responsible for the execution of the legacy system analysis. He should be supported by experts of the legacy system and persons responsible for adjacent systems.

Is generated by

Overall System Specification (see product dependency 4.26)

Overall System Specification (see product dependency 4.25)

Depends on

Overall System Specification, System Architecture (see product dependency 5.59)

5.3.7.11.1 System Outline

The »System Outline describes the rough architecture of the legacy system and its integration into the environment. It indicates objectives and tasks of the system and the context in which the system is used. The system components are described roughly, and the technologies employed are identfied.

In addition, the outline indicates databases on which the system operates, platform and programming language. Adjacent systems with which the system exchanges data and messages are identified, and the interfaces to the legacy system are analyzed and defined.

For a better understanding, the system outline may be complemented by a graphical presentation showing the system in its environment and the system interfaces. The system summary is the basis for the data and interface analysis.

5.3.7.11.2 Functional Overview

The summary of functions describes functionality and business processes supported by the legacy system. If the legacy system is intended to be replaced, the summary of functions provides additional information for specifying the requirements. This ensures that the requirements posed on the new system include all essential functionalities of the legacy system.

5.3.7.11.3 Interface and Dependency Analysis

Legacy systems, particularly legacy information systems, frequently communicate in many ways with a great number of adjacent systems. In the most simple case, the communication is file-based, i.e., a file including data in a specified formart is transferred from the transmitting system to a specified location, where it is read by the receiving system.

An additional communication possibility is the asynchronous transmission and reception of messages by means of messaging systems. In case of a very close coupling of systems, data will be exchanged between the systems within the scope of synchronous calls.

For the above communication forms, a protocol shall be prepared which specifies in detail according to which rules the communication shall be conducted. The protocols will be negotiated and documented with the person responsible for the respective adjacent system

The flow within the system determines the sequence in which the interfaces shall be served. Thus, there are inherent dependencies between the interfaces. These dependencies shall also be identified and documented.

5.3.7.11.4 Data Model

The »Data Model of the legacy system describes how data maintenance was realized in the legacy system. It identifies the affected databases, determines the respective database schemes and documents the results within the scope of their environment. The documentation is prepared analogous to the physical data model of the »Database Design for a new system.

In addition to the data structure, the data quality shall be determined. Based on samples and data copies, it will be determined how many invalid data records exist in the databases of the legacy system and how far these data records impair the workflow.