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Experience

Print View , by: iSee ,Total views: 20 ,Word Count: 6796 ,Date: Wed, 26 Aug 2009 Time: 4:06 PM

Experience

A successful management system is determined by: [50% + 50% of business software] formed, while another 50% of the success of the software [25% of the database + 25% of the programs] of the composition, the database design good or bad is a key. If the enterprise's data comparing the blood necessary for life, then the database design is the application of the most important part of it. Voluminous material related to database design, university degree courses where there are special about. However, as we have repeatedly emphasized, even the best teachers, but the experience than the teachings. So, I have summed up the detour to go over the years and experience, and the Internet is quite a bit of the database design, accomplished professionals who give you some design databases to teach skills and experience. 60 of them selected the best skills, and to the preparation of these techniques have become this, in order to facilitate the indexing of its content is divided into five parts:

Part 1 - Prior to this part of the design of the database lists 12 basic skills, including naming convention and a clear operational requirements. Part 2 - Design a database table a total of 24 guides sexual techniques, covering the fields in the table design, and should avoid common problems. Part 3 - select key option key then how? Here are 10 tips specifically related to system-generated primary key of the correct usage, as well as when and how to index fields to obtain the best properties. Part 4 - to ensure data integrity, to discuss how to maintain the database, clear and robust, how to minimize bad data. Part 5 - a variety of tips are not included in the above four parts of the other techniques, variety, with your database development they hope will be more relaxed. Part 1 - Design a database in the existing environment before the study to design a new database, you should not only be carefully studied business needs but also to examine existing systems. Most of the database project are not built from scratch; Typically, institutions always exist and be used to meet the specific needs of the existing system (which may not automatically calculated). Clearly, the existing system is not perfect, otherwise you will not have to create a new system of. However, the study of the old system allows you to find some minor problems might be overlooked. In general, the study of existing systems is absolutely good for you. Defines a standard object-naming database objects must be defined naming convention. The database table is, from the start of the project is necessary to determine the table name is using the plural or singular form. In addition, the alias of the table should be given to the definition of simple rules (for example, if the table name is a word, take the word alias on the first four letters; if the table name is two words, the two words from each of the first two letters of composed of four letters long alias; if the name of the table formed by the three words, you may wish to scratch and then one from each of the two words in a word from the last two letters out again, the result is composed of four letters long alias, the other in turn and so on) to work with the table, the table can add the prefix WORK_ be appended to the application using the table name. The table column [field] to be used for the key to a set of design rules. For example, if the key is numeric type, you can use as a suffix _N; if a character type, you can use _C suffix. Right column [field] members should use the standard prefix and suffix. Again, if you have a lot of money the table field, you may wish to give each column [field] to add a suffix _M. Also, the date column [field] is best to D_ as the name starts with.

Checklist names, reports, queries were among the names and naming convention. You may soon be these different elements of the name of the database confused. If you insist on naming a unified way the various components of these databases, at least you should name these objects beginning with Table, Query or Report a distinction between the prefix and so on.

If you use a Microsoft Access, you can use qry, rpt, tbl, and mod symbols to identify objects (such as tbl_Employees). I have, and SQL Server when it comes to dealing with tbl used to index the table, but I used sp_company (now used sp_feft_) identifies stored procedure, because sometimes, if I find a better approach tends to keep several copies. I am in the realization of SQL Server 2000 when you use udf_ (or a similar mark) logo I write functions. Gongyushanjishi, must first sharpen his tools with the ideal database design tools, such as: sybase company PowerDesign, she supported the PB, VB, Delphe and other languages, you can connect via ODBC on the market more than 30 popular databases, including dBase , FoxPro, VFP, SQL Server and so on, in the future I will have the opportunity to highlight PowerDesign use. Data Model Resource Book for the sample Patterns are looking for people who can read, "Data Model Resource Book", a book by Len Silverston, WH Inmon and Kent Graziano prepared, is one worth having the best data modeling books. The book includes chapters covering a variety of data areas, such as personnel, institutions and work efficiency and so on. Other You can also refer to: [1] Shi-Xuan Wang Shan Sa with Introduction to Database System (Second Edition) Higher Education Press, 1991, [2] [America] Steven M. Bobrowski with oracle 7 and Client / server computing technology from the Mastering such as translation of Liu Yuan Electronic Industry Press, 1996, [3] Zhou Zhongyuan Information System Modeling Method (B) Electronics and information technology in 1999 3, 1999 Envisioning the future, but can not forget the lessons of the past, I have found that asking the user How do I look to the future changes in demand very useful. This can serve two purposes: First, you can clearly understand the application design should be more flexibility in where to and how to avoid performance bottlenecks; Second, you know that there is no place in advance to determine the needs of the user changes will be surprised like you .

To remember past experiences and lessons! We should also be adopted by developers to share their insights and experiences to help each other. Even if the user that they no longer need any support, we should also in this regard to their education, we have all faced such a moment be nice .. Had to do it. In the physical practice, logical design before physical design of in-depth before the first logical design. With a large number of CASE tools continue to emerge out of your design can achieve very high logic level, you can usually a whole to better understand all aspects of database design needs. Know your business in your hundred percent to determine the system to meet their needs from the customer point of view you do not until ER (entity relationship) model by adding even a data table (how, you do not model? Then please refer to skills 9) . Know your Enterprise business at a later stage of development can save a lot of time. Once you have defined the business requirements, you can make their own decision-making process of many.

Once you think you have made it clear the business content, you'd better with the client to conduct a systematic exchange. Using customer terminology and explain to them what you think and what you hear. It also should be possible to be, and must wait for the vocabulary to express the relationship between the base out of the system. So you can let your customers correct understanding of your own and then do the next step of the ER design. Create a data dictionary and ER diagrams must take the time to create ER diagrams and data dictionary. Of which at least should contain the data type of each field in each table and the primary foreign key. Create ER diagrams and data dictionary is indeed a time-consuming, but for other developers to understand the whole design is absolutely necessary. The sooner the better they can help to avoid in the future to create the possibility of facing the chaos, allowing the database to allow any person to understand clearly how to get the data from the database.

Have an ER diagram, such as the importance of the latest documentation can not be overstated, which shows the relationship between tables is useful, while the data dictionary is illustrated in the use of each field, as well as any possible aliases. Documented on the SQL expression for this is entirely necessary. Create a model of a chart worth a thousand words: the developer must not only read and realize it, but also use it to help themselves and user sessions. Models help to improve the effectiveness of collaboration, so that the initial task of database design is almost impossible to major problems. Models do not have to get very complicated; even be as simple as hand-written on a piece of paper on it. Just want to ensure that the logical relations in the future on which can produce benefits. Input and output from the start with the definition of database tables and fields in the demand (input), the first should check the existing or have been designed out of reporting, query and view (output) in order to determine the output in order to support what is necessary tables and fields in . To give a simple example: If customers need a report sorted according to postal code, sections and summation, you have to ensure that the postcode, including a separate field, rather than making melted into the address field where postcode. Report tips to understand how users typically report data: the batch and online filing of returns? Time interval is daily, weekly, monthly, quarterly, or annually? If necessary, could also consider creating a summary table. System-generated primary key in the report difficult to manage. The user with a system-generated primary key of the table is often used to retrieve the Deputy button will return a number of duplicate data. This retrieval performance is relatively low and easy to cause confusion. To understand customer needs seems this should be obvious, but the demand is from customers (internal and external customers here, from the point of view). Do not rely on the user needs to write down the real needs of the customer's head. You want customers to explain their needs, and along with the continued development, they often ask clients to ensure their needs are still in the development of the purpose of being. A constant truth is: only I have seen before I know what I want is what will inevitably lead to a lot of rework, because the database does not meet customer needs has never been written down standards. Worse still is that you need to explain to them only to your own, but may be completely wrong. Part 2 - Design tables and fields that examine the various changes I will be considered when designing a database to which data fields in the future may be subject to change. For example, the surname is the case (note that is a western name, such as women from the husband's surname after marriage, etc.). Therefore, customer information is stored in the establishment of the system, I tend to a data table in a separate store name field, but also additional fields for starting date and termination date, so that you can keep track of this data entry changes. Use meaningful field names once had a project I have participated in the development, of which inherit from other programmers program, that programmers like to use the instructions on the screen display data language named fields, this is not that bad, but unfortunately, She also likes to use some strange nomenclature, their names using the Hungarian naming and control of serial numbers of the combination of forms, such as cbo1, txt2, txt2_b and so on. Unless you use only the abbreviation for the field names of your system, otherwise the field as much as possible to describe more clearly. Of course, they should not done first, and such Customer_Shipping_Address_Street_Line_1, although the very rich illustrative, but no one wants to type such a long name, the specific scales in your grasp of. Named using the prefix table, if there is a lot more than the same type of field (such as FirstName), you may wish to use a particular table prefix (such as CusLastName) to help you identify the field.

Timeliness of data should including the most recent update date / time field. Time stamp to find data on the cause of the problem, by date to re-processing / reload data and clear the old data were particularly useful. Standardization and data-driven standardization of data is not only convenient but also facilitates their others. For example, if your user interface to access external data sources (files, xml documents, other databases, etc.), you may wish to put the corresponding connection and path information is stored in the user interface support table. Also, if the user interface, like the implementation of the workflow tasks (send e-mail, printing stationery, modify, record status, etc.), then the resulting workflow data can also be stored in a database. Will always be pre-arranged effort, but if these processes using data-driven approach rather than the hard-coded, then the strategy changes and maintenance will be easier. In fact, if the process is data-driven, you can put a large responsibility to the user, by the user to maintain their own workflow process. Standardization does not overdo the word to those not familiar with the standard (normalization) of the people, standardization ensures that the table of the fields are the most basic elements, and this measure will help to eliminate redundant data in the database. There are several forms of standardization, but the Third Normal Form (3NF) are usually considered in terms of performance, scalability, and data integrity to achieve the best balance. To put it simply, 3NF rules: * Each table can only be expressed by a value once. * Each line in the table should be a unique identifier (a unique key). * The table should not be stored depends on other key non-key information. To comply with the standard 3NF database has the following features: There is a set of tables stored by the specialized keys associated data linking. For example, a store customer and its related orders 3NF database may have two tables: Customer and Order. Order table does not contain any information about customer orders associated with, but the table will store a key, the key point to Customer table contains the customer information the line. Also have a higher level of standardization, but more whether the criteria will certainly be better? The answer is not necessarily. In fact, for some projects, and even the introduction of even 3NF database can give too much complexity.

For efficiency reasons, the table is not standardized and sometimes also necessary, so many examples. There was a development of live food analysis software is to use non-standardized form to query the time from an average of 40 seconds was reduced to about two seconds. Although I have to do this, but I am not the data table as a natural non-standard design. The specific operation, but is a kind of derivative. So if Biaochu a problem to re-produce non-standard table is entirely possible. Microsoft Visual foxpro reporting skills If you are using Microsoft Visual FoxPro, you can use a user-friendly field names instead of numbers names: for example, with the Customer Name instead of txtCNaM. Thus, when you use the wizard [Wizards, the people of Taiwan known as the 'Wizard'] to create forms and reports, their names will make those who are not programmers are more easy to read. Not active or not used indicator to add a field where the records that are no longer active in the business Tingyou useful. Whether customers, employees, or someone else doing so can help to re-run the query when filtering active, or inactive. It also eliminates the use of a new user in the data some of the problems faced by, for example, some records may no longer be used for them, and then removed when a certain degree of preventive effect. Use the definition of the role of entities belonging to a class of the column [field] in the need to belong to a particular class or category of things to do with a specific definition of the role, you can use to create the role of physical association between a specific time, which can be self-documenting. The implication is not so PERSON entity with the Title field, but rather that, why not PERSON entities and PERSON_TYPE entities to describe the officer? For example, when John Smith, Engineer upgraded to John Smith, Director and finally climbed to John Smith, CIO of the high, and all you have to do is to change the two tables of the relationship between PERSON and PERSON_TYPE keys, while increasing a Date / Time field to know when the change is to happen. In this way, you PERSON_TYPE all the PERSON table contains the possible types, such as Associate, Engineer, Director, CIO or CEO and so on. There are one alternative is to change the title PERSON records to reflect the new changes, but this way the timing can not track individual location of a specific time. Use of common data entities, naming institutions the easiest way to organize data is to use common names, such as: PERSON, ORGANIZATION, ADDRESS and PHONE so on. When you used the general name of these combinations or create a specific corresponding vice entities, you will get to use a special version of his. The beginning of the main reason for using a general term for all specific users to be able to abstract things concrete. With these abstractions that you can identify the first two used their own special name, for example, PERSON may be Employee, Spouse, Patient, Client, Customer, Vendor, or Teacher, etc.. Similarly, ORGANIZATION may also be MyCompany, MyDepartment, Competitor, Hospital, Warehouse, Government and so on. Finally ADDRESS can be specified as a Site, Location, Home, Work, Client, Vendor, Corporate, and FieldOffice so. Terminology commonly used in the abstract to identify the type of things will allow you to meet the business requirements associated with the data gained tremendous flexibility, while doing so can significantly reduce the amount of data storage required for redundancy. Users from around the world used in the design of network or have other international character of the database, we must remember that most countries have different field formats, such as postal code, and some countries, such as New Zealand, said there would be no postal code a . Duplication of data need to adopt separate tables if you find yourself repeating the input data, create a new table and a new relationship. Each table should be useful to add three fields * dRecordCreationDate, in the vb under the default Now (), while in SQL Server under the default GETDATE () * sRecordCreator, under the SQL Server defaults to NOT NULL DEFAULT USER * nRecordVersion, recorded version of the mark; contribute to accurate description of the record null data or data loss occurs because of the address and telephone number of fields with a short description of the street address on a line record is not enough. Address_Line1, Address_Line2 and Address_Line3 can provide greater flexibility. Also, telephone numbers and e-mail address is best to have their own data tables, during which the type and marked with its own category.

Standardization will happen too cautious to do so may lead to performance problems. Although the address and telephone tables can usually achieve the best separation, but if you need frequent access to such information, perhaps stored in the parent table in the preferred information (such as Customer, etc.) more appropriate for some. Non-standardized and accelerated access to a compromise between there is a certain significance. Use more than one name field I am very surprised that many people in the database to remain a field Jiugei name. I think only a developer would have just started to do so, but in fact this practice is very common online. I suggest that should be first and last name as the two fields to deal with, and then check the time then they are combined.

I am most commonly used in the same table to create a calculated column [field], it can automatically connect through the standardized field, so that when the data changes, it also followed the change. However, doing so in a very clever use of modeling software Cai Xing. In short, the method used to connect the field can effectively isolate the user interface for applications and developers. Beware of mixed-case object names and special characters in the past, one of the things I was most annoyed is that the database, there are mixed-case object names, such as CustomerData. This problem from the Access to Oracle database exist. I do not like using this case-mix of the object naming method, the results also have to manually change the name. Think about it, such a database / applications can be mingled with a more powerful database that day? Make use of all caps and includes breaks under the designated name of a better readability (CUSTOMER_DATA), the object name should never leave a space between the characters. Be careful to retain the word to ensure that your field names do not and retention of words, the database system or access method commonly used conflict, for example, I recently prepared an ODBC connection program, there are tables, which will use as an illustration of the DESC field names. The consequences can be imagined! DESC is retained after the word DESCENDING abbreviation. Table of a SELECT * statement Daoshi can be used, but I got in return was a lot of useless information. To maintain the consistency of field names and types in the name field and specify the data type for the time we must ensure consistency. If the field in a table called agreement_number, you do not change his name in another table ref1. If the data types in a table is an integer, it may do in another table into a character has. Remember, you done everything he lived for his own, other people should do with your database. Carefully choose the number type in SQL using smallint and tinyint type to be especially careful, for example, if you want to take a look at the total monthly sales, the total amount of your field type is smallint, then the total amount of more than $ 32,767 if you can not calculate operation of the . Remove the tag in the table contains a deletion tag field, so lines can be marked for deletion. Do not separate in a relational database to delete a row; the best use of clear procedures for data integrity but also to carefully maintain the index. Avoid the use of trigger flip-flop features can often be achieved by other means. In the debugging program may be interfering with the trigger. If you really need to use triggers, you'd better focus on documenting it. Contains the version of the system suggest that you introduce in the database, version control mechanism to determine the version of the database in use. In any case you have to realize this requirement. Over time, the user's needs will always change. Ultimately may be required to modify the database structure. Although you can check for new field or an index to determine the version of the database structure, but I find the version information is not directly stored into the database is more inconvenient? . Leave enough margin to the text field of type ID text field, such as customer ID or order number, etc., should be set higher than the general imagination, because time is not long since you'll probably want to add extra characters and endless embarrassment . For example, suppose your customer ID is 10 digits long. Then you should set the length of the database table fields 12 or 13 characters long. This is considered a waste of space? There is a point, but do not you think so many: a field of three characters longer than 1 million records, together with the index case that was only occupied the entire database, more than 3MB of space. However, they do not need the additional space occupied in the future reconstruction of the entire database can be achieved an increase of the size of the database. ID card number from 15 into 18 is the best and most tragic example. Column [field] naming techniques we have found that if you give each table column [field] members have adopted a unified prefix, then the time in the preparation of SQL expression will be greatly simplified. It would also does have shortcomings, such as undermining the role of automated tools for table join, the latter of public Column [field] were linked with some of the database, but even these tools sometimes do not have connection error Well. To give a simple example, assume that there are two tables: Customer and Order. Customer table prefix is cu_, so the table name of the sub-paragraph as follows: cu_name_id, cu_surname, cu_initials and cu_address so. Order the table prefix is or_, so sub-section names are: or_order_id, or_cust_name_id, or_quantity and or_description so. This selected all the data from the database of the SQL statements can be written as follows: Select * From Customer, Order Where cu_surname = "MYNAME"; and cu_name_id = or_cust_name_id and or_quantity = 1 in the absence of these prefixes are written in circumstances like this (using an alias to distinguish between): Select * From Customer, Order Where Customer.surname = "MYNAME"; and Customer.name_id = Order.cust_name_id and Order.quantity = 1 the first one SQL statement, not a small number of characters typed. However, if the query involves five or even more columns to the table [field] you know this technique more useful. Part 3 - select key and index data mining to be pre-planned where I was once a client departments to handle more than 80,000 copies of contact at the same time fill in the necessary data for each client (this is definitely not a small living). I have to also identify a group of customers as a marketing target. When I started to design tables and fields most of the time, I tried not to the main index has increased by a lot of fields in order to speed up the database speed. Then I realized that a specific group of queries, and information extraction are neither accurate nor fast speed. The results had to rebuild the main index and merge the data field. I found that there is a direct scheme is the key - when I want to create a system when this type of check numbers to be used as the primary index field do? Can I use fax number to retrieve, but it is almost like the same type of system is not important to me. The latter as the main field, the database updated and re-indexing and retrieval on the much quicker.

Operational Data Warehouse (ODS) and data warehousing (DW) data in both environments there is a difference between the index. In the DW environment, you have to consider sales department is how to organize sales activities. They are not database administrators, but they determine the table of key information. Here the designer or the database staff database structure should be analyzed to identify and correct the output performance between the best conditions. Using the system-generated primary key of these same skills one, but I feel it is necessary to repeat them here to remind you. If you are always in the design of a database when using system-generated key as the primary key, then you actually control the integrity of the database indexes. In this way, the database and non-interrupting mechanism to effectively control the storage of data in each row access. Using system-generated key as the primary key there is an advantage: When you have the same key structure, to find the logical flaw is easy. Decomposition of the index field is used to name the field to isolate and contain user-defined fields to support the statements, consider the decomposition of the other fields (or even the primary key) as its constituent elements so that users can index them. The index will speed up SQL and Report Builder script execution speed. For example, I usually have to use the case of SQL LIKE expression to create a report, as case number field can not be broken down into year, serial number, case type and the defendant code elements. Performance will deteriorate. If the year and type of field can be decomposed into an index field, then these statements will be up and running much quicker. Key Design Principle 4 * for the association to create a foreign key field. * All keys must be unique. * Avoid the use of composite keys. * Foreign key is always associated with a unique key field. Do not forget the index index is to get data from the database, one of the most efficient manner. 95% of the database performance problems can be solved using indexing technology. As a rule, I usually use the logical primary key into a unique group index, keys on the system (as stored procedures) using only non-grouping indexes, foreign key columns for any [field] use of non-grouping indexes. However, the index is like salt, too much food on the salty. You have to consider how much space a database, table how to access, as well as these visits are mainly used for reading and writing.

Most databases are automatically created the index primary key field, but do not forget the index foreign keys, they are also frequently used keys, such as running queries show the main table and all the associated tables on the lingua franca of certain records. Also, do not index memo / note field, not an index of large fields (there are many characters), to do so will make the index take up too much storage space. Do not index small tables commonly used for small data tables not to set any keys, if they often do not insert and delete operations that were made even more. Of these insertion and deletion operations of the index maintenance may consume more than scanning the table space of time. Do not put Social Security Number (SSN) or identity card number (ID) selected as the key to never Do not use SSN or ID as a database key. In addition to privacy reasons other than to notify the government increasingly tend to SSN or ID are not allowed except for purposes other than income-related, SSN, or ID required manual input. Never use the manual input of keys as the primary key, because once you enter the wrong, you only can do is delete the entire record and then start from scratch.

I crack other people's programs, I see a lot of people have SSN or ID has also been used as a serial number, of course, although doing so is illegal. And people also know that this is illegal, but they have used to it. Later, with the increase in identity theft crimes, my peers are now suffering from a large booth in the data the SSN or ID to delete. Do not use the user's key in determining the use of what key field as the table when the user will be sure to be careful to edit the field. Under normal conditions, do not select the user-editable field as key. This will force you to take the following two measures: * To create a record of the behavior of the user edit the field restrictions. If you do, you may find that your application needs a sudden change in the business, and users need to edit non-editable fields that lack sufficient flexibility. When a user input data until after the record-keeping system, a problem discovered how should they think? Remove the reconstruction? If the record is not renewal, allow users to go away? * Detect and correct some key conflict. Typically, the fee also Gao Ding-point effort, but from a performance point of view the cost of doing so is more significant. Also, the keys may force you to correct break your data and business / user interface layer segregation. They still revert to the old saying: Do you design to adapt to the user instead of allowing the user to adapt to your design.

Let the primary key with the renewable nature of reason is that the pattern of relationships, the primary key to achieve the association between the different tables. For example, Customer table has a primary key CustomerID, and the customer's orders are stored in another table. Order the table's primary key may be OrderNo or OrderNo, CustomerID and date combination. Whether you choose which button set, you need to store in the Order table, CustomerID to ensure that you can give the user placing an order to find records of their orders. Customer table if you modify the CustomerID, then you must find all related Order records in the table to modify. Otherwise, some orders will not belong to any client - the integrity of the database even finished. If the index the integrity of the rules applied to the table one, then do not write code and add a large number of deleted records of the case is almost impossible to change a key and a record of all the associated database records. And this process is often the error arisen so should be avoided. Optional key (candidate key) key to remember that sometimes call the shots, query data, not machines but people. If you have an optional key, you may be key to further use it call the shots. In that case, you will have the ability to build strong index. This can prevent the use of the database were forced to connect to the database to the appropriate filter data. Strict control over the domain table in the database, this load is more prominent. If the optional key really useful, and that is the main key to reach the standard. My view is that if you have an optional bond, such as the national table of state_code, you do not change the existing unique key can not be created on the follow-up key. You have to do is to create nothing more than worthless data. If you follow-up due to excessive use of table keys [Alias] associated with the establishment of such a table, working load may need to consider about the whole thing really. Do not forget the majority of the database indexes of foreign keys the primary key field is automatically created. But do not forget the index the foreign key field, they are you want to query the main table records and its associated records will be used each time. Also, do not index memo / notes field and do not index a large text field (many characters), this index will let you take a lot of database space. Part 4 - to ensure data integrity using constraints rather than a mandatory data integrity business rules, if you are in accordance with business rules to deal with demand, then you should check the business-level / user interface: If the business rules after the change, then only need to be updated can be. If the demand stems from the need to maintain data integrity, then the database level, a need to impose restrictions. If you're really in the data layer using constraints, you have to ensure that there are a way to update the reasons can not be bound by checking the language used to inform users to understand user interface. Unless your name is very long field, or field name itself is not enough.

Whenever possible, please use the database system data integrity. This includes not only be achieved through standardization of data integrity but also the functionality. When it comes to writing the data to increase the trigger to ensure the accuracy of the data. Do not rely on the business layer to ensure data integrity; it can not be guaranteed between tables (foreign keys) so it can not impose on others the integrity of the integrity of the rule-based. Distributed data systems to distributed systems, you decide whether to copy all the data in each site, or the data stored in one place should be preceded by an estimate of the next five years or 10 years, the amount of data. When you send data to other sites, the best field in the database set up some tags. In the destination site, after receipt of your data to update your tags. To carry out data transmission, please write your own batch or scheduler to run a specific time interval and not allow users to transfer data after a day's work. Maintenance of the local copy of your data, such as the calculation of constant and interest rates, set the version number to ensure the data at each site are identical.(?),。。。,,。。,。。,。/。。,,。,。。。。:、。5 - 、、、、。

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