On the Codd semantics of SQL nulls

Theoretical models used in database research often have subtle differences with those occurring in practice. One particular mismatch that is usually neglected concerns the use of marked nulls to represent missing values in theoretical models of incompleteness, while in an SQL database these are all denoted by the same syntactic

object. It is commonly argued that results obtained in the model with marked nulls carry over to SQL, because SQL nulls can be interpreted as Codd nulls, which are simply marked nulls that do not repeat. This argument, however, does not take into account that even simple queries may produce answers where distinct occurrences of

do in fact denote the same unknown value. For such queries, interpreting SQL nulls as Codd nulls would incorrectly change the semantics of query answers. To use results about Codd nulls for real-life SQL queries, we need to understand which queries preserve the Codd interpretation of SQL nulls. We show, however, that the class of relational algebra queries preserving Codd interpretation is not recursively enumerable, which necessitates looking for sufficient conditions for such preservation. Those can be obtained by exploiting the information provided by NOT NULL constraints on the database schema. We devise mild syntactic restrictions on queries that guarantee preservation, do not limit the full expressiveness of queries on databases without nulls, and can be checked efficiently.     

Automating data exchange in process choreographies

Communication between organizations is formalized as process choreographies in daily business. While the correct ordering of exchanged messages can be modeled and enacted with current choreography techniques, no approach exists to describe and automate the exchange of data between processes in a choreography using messages. This paper describes an entirely model-driven approach for BPMN introducing a few concepts that suffice to model data retrieval, data transformation, message exchange, and correlation – four aspects of data exchange. For automation, this work utilizes a recent concept to enact data dependencies in internal processes. We present a modeling guideline to derive local process models from a given choreography; their operational semantics allows to correctly enact the entire choreography from the derived models only including the exchange of data. Targeting on successful interactions, we discuss means to ensure correct process choreography modeling. Finally, we implemented our approach by extending the camunda BPM platform with our approach and show its feasibility by realizing all service interaction patterns using only model-based concepts.     

ERP环境下BOM的构造及其应用研究

介绍了在ERP软件中BOM的构造 ,通过对某厂实例的分析 ,应用单层BOM和ORACLE的SQL语句 ,实现了通过子件反查最终产品的实际应用问题     

可参数化网络零件库的研制与开发

建立了基于C/S结构的网络环境下的可参数化三维零件库系统,建立了标准件和非标准件库.本文以"联轴器、键、轴"的装配体为例,对部件参数化技术进行介绍,并对在Internet环境下零件库的建立进行研究.该零件库具有可扩充性,可涵盖机械领域中所有标准零件以及企业内部经常使用或加工的非标准件,是一种较实用的企业应用软件.     

基于WEB数据库的煤矿机电信息管理平台的设计与实现

用ASP网站设计、SQLserver2 0 0 0数据库软件和VisualBasic可视化软件 ,采用ADO技术开发了机电信息管理平台。以煤矿机电设备信息和输配电数据信息为基底 ,集成设备管理人员信息和使用情况为属性数据构建数据库。集信息存储、打印、更新、管理、查询、分析 ,Internet网上传输功能 ,实现网上的资源共享和网络办公     

煤矿机电设备管理信息系统设计研究

采用VB．NET作为前端的开发工具，采用SQL Server 2000作为后台数据库，开发了一个面向具体应用的管理信息系统，来完成对煤矿企业机电设备信息的整理、维护和保存。给出了该煤矿机电设备管理信息系统的模块功能、数据库、字段功能、后台数据库结构、窗体设计思路。     

基于GIS的测绘资料管理系统设计与实现

介绍了合肥市测绘设计研究院资料管理系统的数据结构组织及主要功能的实现，阐述了利用地理信息技术和大型数据库技术对档案资料进行科学、有序管理的思路和方法。     

基于Visual C＋＋的水声目标数据库设计

针对水声目标实测数据量庞大,LOFAR和DEMON分析计算量大的问题,设计了一个基于Visual C＋＋6．0的数据库管理系统。管理系统通过ADO接口实现与SQL Server 2005数据库管理程序的数据交换,保证了数据稳定存储和高效传输。通过内存映射文件技术,实现了对大数据文件的快速读取。采用CPU与GPU并行计算进行了LO-FAR和DEMON分析,实现了LOFAR和DEMON谱图的实时显示。整个数据库管理系统操作简洁高效,可靠性高,具有广泛的实际应用价值。     

基于ERP的水泥工程项目管理系统设计与开发

文章完成了基于ERP的水泥工程项目管理系统的总体方案设计,体系结构和数据库设计,主要功能模块的软件设计。     

基于B/S与C/S协同服务的高校资产与实验室综合管理平台的设计实现

深入研究如何通过B/S、C/S协同服务技术设计并实现一个可供高校资产管理部门对资产以及实验室进行综合管理的平台。结合使用WPF(Windows Presentation Foundation)、SliverLight、WCF(Windows Communication Foundation)服务等技术进行系统的协同架构设计。通过多种技术的结合,实现一个屏蔽各种技术之间差异、可为高校日常的资产管理提供快速便捷服务的综合业务办公平台,解决当前高校资产管理混乱、效率低下的现状,使高校固定资产管理水平再上新台阶,迈向科技化、信息化新阶段。