The organization's agility represents its ability to respond fast to changes by the transformation and/or optimization of business processes, therefore it is a key factor in the competitiveness and growth of the organization. Bearing in mind the importance and expansion of the use of digital technologies, the organization's agility can be compromised if the digital strategy and IT resources are not flexible enough to adequately respond to changed business conditions. Service-Oriented

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... e (SOA) is an approach to the development of business software systems that promote better alignment of business and digital strategy, i.e. business goals and IT resources, enabling the organization to faster adapt and respond to changes in the business environment. However, the success of the SOA initiative depends largely on the choice of delivery strategy and the way services are identified, as well as the choice of an approach in the implementation of SOA, given the way of integration and communication between services. The middle-out delivery strategy is a compromise between top-down and bottom-up approach. This approach, at the same time, supports SOA implementation guided by a strategic vision, business strategy and strategical goals, and use of existing IT resources with focus on urgent requirements and tactical goals. Realization of middle-out delivery strategy is based on several small, iterative SOA projects, where each individual SOA project was implemented to meet specific business goals and requirements. On the other hand, in order to respond to new challenges and requirements of the digital era regarding the distribution, scaling and increased complexity, SOA evolves towards increasing agility and a simpler, service-based approach at business and technical level. This avoids the complexity of the Enterprise Service Bus (ESB) as an integrator in communication between the services. Avoiding the ESB as a universal mediator and orchestrator in communication between the services enables a serious shift in the delivery speed and scalability of software solutions. This paper, in general, discusses the ways of more efficient alignment of business and digital enterprise strategies based on the implementation of SOA initiatives for the development of business software systems. Within the framework of the research of this paper, the very significant challenges and best practices are identified and clearly distinguished, as well as the advantages and disadvantages, related to the architectural and methodological aspects of the implementation of the SOA middle-out delivery strategy and service-based approach. The complete research effort, as well as the results obtained, is dedicated to the effective implementation of SOA in the context of the development of business software systems. The results of the work include consideration of the evolution of SOA-based approaches in the digital era, leading to increased agility and a reduction of complexity.